1. health and fitness
2. disease

592
REVIEW ARTICLES
Outcome of Medical Treatment of Bacterial Abscesses Without Therapeutic
Drainage: Review of Cases Reported in the Literature
David M. Bamberger
From the Section of Infectious Diseases, University of Missouri-Kansas
City School of Medicine, Kansas City, Missouri
Bacterial abscesses usually require drainage for cure. Reasons postulated for the ineffectiveness of antibiotics in the
treatment of abscesses include the presence of stationary-phase
organisms, low pH, high protein content, the large number
of bacteria within abscesses, ionic composition, low oxygen
tension, sequestration of bacteria within leukocytes, low
abscess zinc concentrations, and the presence of antimicrobial
agent-deactivating enzymes [1]. Antimicrobial therapy is generally ineffective in experimental models of suppurative infections when initiation of therapy is delayed for ;?:24 hours [2].
Since the 1970s there has been an increasing number of
reports of other abscesses, especially those involving the brain,
liver, and kidney, that have responded to antimicrobial therapy
without the need for a drainage procedure. This report reviews
the literature regarding medical treatment ofbacterial abscesses
in order to determine the extent of the clinical experience documented to date and to define the clinical, microbiological, and
therapeutic features of abscesses responding to medical therapy. Since routine initial therapy for lung and tubo-ovarian
abscesses no longer includes a drainage procedure, these cases
were excluded.
See the editorial response by Lerner on pages 604- 7.
Methods
It has long been recognized that lung abscesses respond to
prolonged courses of antimicrobials without formal surgical
drainage. Since many lung abscesses have air-fluid levels that
were observed radiographically, suggesting bronchial communication, it is likely that lung abscesses spontaneously drain
via the bronchial tree. It has also been well recognized that
most abscesses of the tubo-ovarian region-especially those
<8 em in diameter-respond to antimicrobial therapy without
the need for surgical drainage [3], perhaps again because spontaneous drainage occurs via the fallopian tubes.
Received 3 October 1995; revised 1 May 1996.
Presented in part at the 33rd Annual Meeting of the Infectious Diseases
Society of America, held 16-18 September 1995 in San Francisco.
Reprints or correspondence: Dr. David M. Bamberger, Red 4 Unit, UMKC
School of Medicine, 2411 Holmes Street, Kansas City, Missouri 64113.
Clinical Infectious Diseases 1996;23:592-603
© 1996 by The University of Chicago. All rights reserved.
1058--4838/96/2303 - 0026$02.00
A MEDLINE search of the literature from 1966 to August
1994 was done to find all English-language reports of bacterial
abscesses treated medically, without a therapeutic drainage procedure. Additional cases were included by review of the references of the reports found in the MEDLINE search. Cases were
excluded if (1) the cause of the abscess was either a higher
bacterium (Nocardia or Actinomyces species) or a mycobacterium, (2) the outcome could not be determined from the report,
and (3) medical management was not attempted. When it was
evident that the case had been reported more than once, the
second report was excluded.
Cases involving small-volume «5 mL) diagnostic aspirations were not excluded, nor were those involving largervolume aspirations if multiple abscesses were present and at
least one abscess was not aspirated. In addition, an aspirate of
up to 15 mL was acceptable when it was clear from the report
that this volume represented <25% of the total abscess volume.
For each reported case, a form was completed that included
information regarding the clinical and microbiological features of
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The usual treatment of bacterial abscesses, except lung or tubo-ovarian abscesses, includes therapeutic drainage. Increasing evidence suggests that some abscesses respond to antimicrobial therapy
without drainage. To study this issue, a MEDLINE search of the literature (1966-1994) was performed for cases of bacterial abscess in which treatment without definitive drainage was attempted.
Four hundred sixty-five cases were identified. The most commonly involved organs were the liver,
brain, and kidney. The success rate of antimicrobial therapy was 85.9%. Factors that predicted a
less favorable outcome were abscess diameter of ~5 em (odds ratio [OR] = 37.7; P = .0003),
involvement of ~1 organism (OR = 5.2; P = .014), presence of gram-negative bacilli (OR = 3.4;
P = .022), length of therapy of <4 weeks (OR = 49.1; P < .0001), and use of an aminoglycoside
as the only active agent (OR = 11.8; P = .008). Many bacterial abscesses can be treated without
drainage; abscess size, the organisms involved, and therapy utilized may influence outcome.
em
Treatment of Abscesses Without Drainage
1996;23 (September)
Table 1. Organ involvement in 465 cases of bacterial abscesses
treated without therapeutic drainage.
No. (%) of patients
Organ or site of
involvement
Liver
Brain
Renal
Epidural space
Subperiosteum of orbit
Spleen
Pancreas
Heart or heart valves
Seminal vesicle
Total
Successfully
treated
176(37.8)
143 (30.8)
55 (11.8)
44 (9.5)
19 (4.1)
17 (3.7)
6 (1.3)
5 (1.1)
1 (0.2)
143 (81.2)
128 (89.5)
44 (80.0)
40 (90.9)
18 (94.7)
IS (88.2)
6 (l00)
5 (l00)
1 (l00)
Results
Four hundred sixty-five cases of abscesses treated medically
were found in 138 reports in the literature published from 1966
to August 1994 [4-142]. Three hundred ninety-nine (85.8%)
of these patients were successfully treated without the need for
therapeutic drainage. The ages of patients ranged from neonatal
to 87 years, with a median age of 31 years.
The organs involved in the 465 patients with bacterial abscesses
are shown in table 1. The treatment success rate varied between
80% (in the 55 cases of renal abscesses) and 100% (in the few
cases of heart/heart valve, pancreatic, and seminal vesicle abscesses). There was no statistically significant relationship between organ type and treatment success rate (P = .087, X2 test).
The clinical features and abscess characteristics of the 465
patients are shown in table 2. Because this was a literaturereview study and not all reports offered information about the
characteristics included in the table, the number of patients
analyzed for each feature varied. Data from reports in which
these clinical features were described showed that most of the
patients were febrile and had pain at the abscess site. The
median duration of symptoms was 8 days (range, 1-180 days).
The median abscess size was 3 em (range, 0.5-13 em). Ninetyfive patients had multiple abscesses.
One hundred seventy-eight cases had a positive blood culture, a positive gram stain, or growth of organisms in a cultured
specimen from either the abscess or a normally sterile contigu-
ous site. Eighteen patients [19, 21, 22, 36, 40, 41, 49, 63, 69,
89,94, 105, 107, 119, 121, 130, 135, 142] were known to
have received antimicrobial therapy when their positive culture
specimens were obtained, including abscess aspirates (12),
blood (3), and contiguous-site specimens (5). Eight patients
[20,29,46,47,68,79,108,141] were known not to be receiving antimicrobial therapy when culture-positive specimens
were obtained, including abscess aspirates (1), blood (4), and
contiguous-site specimens (3). The specific timing of antimicrobial therapy and the obtaining of culture specimens could
not be ascertained for the remaining 152 patients whose cultures were positive.
In the reports of 169 of the 178 cases involving positive
cultures, the specific organism genus was mentioned. One hundred seventy-nine patients were known to have blood cultures
performed, and for 92 the results were positive. Sixty-two patients had diagnostic aspirations performed, and cultures of 54
of these aspirates yielded growth. For four patients [5, 48, 80,
89], the diagnostic aspirate volume was >5 mL (range, 6-15
ml.). Microbiological findings included growth of> 1 organism
(14 patients), a single gram-positive aerobe (90), a single gramnegative aerobe (49), and a single anaerobic organism (16). It
was not possible to determine from the reports the type and
adequacy of the microbiological methodology.
Each feature was analyzed, and three correlated with a successful outcome: abscess size of <5 ern, presence of only one
bacterial organism, and lack of involvement of aerobic gramnegative bacilli. It is noteworthy that of the 51 cases in which
the abscess size was reported to be <5 em, all were successfully
treated without therapeutic drainage.
The clinical and microbiological features were analyzed according to the four most commonly involved organs (liver, brain,
kidney, and epidural space) and are presented in table 3. More
patients with brain or epidural-space involvement had evidence of
organ dysfunction than did patients with liver or renal abscesses.
Among the patients with brain abscesses, 46 had focal neurological signs or symptoms, 28 had mental status changes, and 16 had
seizures. Among the patients with epidural-space infections, 6 had
bowel or bladder incontinence, 6 had extremity weakness, 4 had
paraplegia or tetraplegia, and 2 had a sensory level. Fifty-eight
percent of liver abscesses were ~5 em, a feature not noted in
any ofthe cases of brain, renal, or epidural abscesses. The outcome
for patients with liver abscesses of ~5 em was less favorable
than for patients with smaller abscesses.
Only a minority of patients had more than one organism isolated. When analyzed according to organ involvement, the lower
success rate for polymicrobial infections was statistically significant only for renal abscesses. Although the success rate was lower
among all patients with abscesses due to aerobic gram-negative
bacilli than among patients whose abscesses did not involve such
bacilli, differences did not reach statistical significance when analyzed according to type of organ involvement.
Radiographic procedures indicative of the presence of an abscess are shown in table 4. Many of the larger reports did not
specify which type of procedure was used for each individual
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the case, the antimicrobial regimen utilized, and the outcome.
A successful outcome was defined as clinical improvement and
survival, without the need for therapeutic drainage. Patients were
considered to have undergone attempted medical therapy if (1)
they were treated for a known bacterial abscess before death and
(2) received antimicrobial therapy for at least 24 hours before
treatment failure was diagnosed (because of the need for drainage)
in cases of clinical deterioration or for at least 72 hours in cases
of clinical stability. Groups were compared statistically with a
two-tailed Fisher's exact test or a X2 test.
593
594
em 1996;23 (September)
Bamberger
Table 2. Clinical and microbiological features of 465 patients with bacterial abscesses treated without therapeutic drainage.
Number (%) of patients
Feature
NOTE.
With
feature
With feature
and successful
outcome
Without feature
and successful
outcome
188
156
178
142
171 (91.0)
130 (83.3)
99 (55.6)
59 (41.6)
159 (93.0)
121 (93.1)
96 (97.0)
55 (93.2)
16(94.1)
24 (92.3)
75 (94.9)
77 (92.8)
78
215
27 (34.6)
95 (44.2)
20 (74.1)
88 (92.6)
51 (100)
110 (91.7)
37.7; 2.1-691; .0003
0.88; 0.32-2.39; 1.00
169
169
169
169
14 (8.3)
91 (53.8)
58 (34.3)
23 (13.6)
9
80
46
22
140 (90.3)
69 (88.5)
103 (92.8)
127 (87.0)
5.18; 1.54-17.5; .014
1.054; 0.41-2.69; 1.00
3.39; 1.3-8.77; .022
0.30; 0.039-2.39; .32
(64.2)
(87.9)
(79.3)
(95.6)
OR; 95% CI; P value
1.21; 0.15-9.90;
0.89; 0.18-4.39;
0.59; 0.13-2.67;
0.93; 0.25-3.47;
1.00
1.00
0.70
1.00
P values were determined with a two-tailed Fisher's exact test.
patient. CT, ultrasonography, and nuclear medicine scans were
used in the diagnosis of liver, renal, and splenic abscesses. Most
of the brain abscesses and all of the subperiosteal orbit abscesses
and pancreatic abscesses were diagnosed by CT. Epidural abscesses were diagnosed by CT, MRI scans, and myelography.
The organisms isolated from the 169 patients whose cultures
yielded microbes are shown in table 5. The most common
organisms isolated were Staphylococcus aureus (from 58 of
the 169 patients), Escherichia coli (26), and viridans streptococci (20). There were marked differences in the bacteria observed in the different organs (tables 3 and 5). Aerobic grampositive, aerobic gram-negative, and anaerobic organisms were
equally mixed in liver abscesses. Brain abscesses were due to
mostly aerobic gram-positive organisms, especially S. aureus
and viridans streptococci, and anaerobes were also frequently
observed. Aerobic gram-negative pathogens were most common in renal abscesses, but S. aureus was also observed in 11
of 32 patients. S. aureus was observed in 22 of the 30 patients
with epidural abscesses, and Salmonella species were the most
frequent isolates from patients with splenic abscesses.
The length of the antimicrobial regimen was documented in
186 of the 465 reports. The median duration of therapy was
42 days, within a range of 3 days to > 1 year. One hundred
thirty-seven patients received antimicrobial therapy for >4
weeks, and the outcome was successful for 136. Of the 49
patients who received therapy for ::.=::;4 weeks, it failed for 13
(OR = 49.1; 95% CI, 6.2-388; P < .0001): 7 with liver
abscesses, 3 with brain abscesses, and 1 each with a renal,
subperiosteal-orbit, and epidural-space abscess. These data may
be difficult to interpret, however, since the course of antimicrobial therapy often was discontinued or shortened when its failure was noted. Only one patient clearly relapsed after a short
course (10 days) of antimicrobial therapy, and that patient's
condition subsequently responded to a 52-day regimen.
Of the 219 cases in which the type of antimicrobial regimen
was specified, therapy failed in only 15. Information about
the patients treated successfully, classified according to organ
involvement, microbial etiology, and antimicrobial usage, is
provided in table 6. Forty-four of 47 patients treated with a
,B-lactam drug alone, 59 of 66 patients treated with a ,B-lactam
drug plus an aminoglycoside, 75 of 83 patients treated with an
aminoglycoside, 20 of 21 patients given metronidazole (often
in combination), and 14 of 14 patients given rifampin (often
in combination) were treated successfully.
Information about the patients whose medical therapy failed
is provided in table 7. Among the 59 patients who received
an aminoglycoside as treatment for an abscess of which the
microbiological cause was known, medical management failed
for 8, and for 4 of these patients the aminoglycoside was the
only administered agent noted to be active against at least one
of the pathogens (P = .0084; OR = 11.75; 95% CI, 2.1-65.7
[vs. 4 of 51 patients for whom the aminoglycoside was used
but was not the only active agent]).
Thirty patients, of which 28 had brain abscesses, were known
to have received corticosteroids in addition to antibiotics. The
outcome for 29 of these patients was successful (OR = 5.09;
95% CI, 0.68-38.1; P = .102 [vs. the 370 successful outcomes
among 435 patients not known to have received corticosteroids]).
Among the reports of the 399 cases treated successfully, 79
provided information regarding the length of therapy before
resolution of fever. The median duration of antimicrobial therapy prior to resolution of fever was 5 days (range, 0-49 days).
In 23 cases fevers resolved in ~2 weeks.
Discussion
The most important information from these data is the large
number of abscesses successfully treated without therapeutic
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Symptom
Fever
Pain
Organ dysfunction
Duration of symptoms, ~ 14 d
Abscess characteristics
Size, ~5 cm
Multiple
Isolate(s)
>1
Aerobic gram-positive coccus
Aerobic gram-negative bacillus
Anaerobe
Analyzed for
presence of
feature
ern 1996;23 (September)
595
Treatment of Abscesses Without Drainage
Table 3. Clinical and microbiological features of 176 patients with liver abscesses, 143 patients with brain abscesses, 55 patients with kidney
abscesses, and 44 patients with epidural-space abscesses, all treated without therapeutic drainage.
Number (%) of patients
With
feature
With
feature
and
successful
outcome
Without
feature
and
successful
outcome
P value
(OR; 95% en
Site of abscess
Fever
Liver
Brain
Kidney
Epidural space
Liver
Brain
Kidney
Epidural space
Liver
Brain
Kidney
Epidural space
34
64
36
22
26
36
35
31
19
72
21
28
33 (97.0)
52 (82.8)
36 (100)
19 (86.3)
19 (73.1)
27 (75.0)
34 (97.1)
31 (l00)
1 (5.3)
68 (94.4)
0
15 (53.6)
26 (78.8)
50 (96.2)
35 (97.2)
19 (100)
13 (68.4)
27 (100)
33 (97.1)
31 (100)
1 (100)
66 (97.1)
0
15 (100)
0
12 (100)
0
3 (100)
6 (85.7)
9 (100)
I (100)
0
16 (88.9)
4 (100)
20 (95.2)
13 (100)
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
Liver
Brain
Kidney
Epidural space
Liver
Brain
Kidney
Epidural space
Liver
Brain
Kidney
Epidural space
23
56
21
19
31
30
2
0
55
94
19
17
11 (47.8)
22 (39.3)
9 (42.9)
10 (52.6)
18 (58.0)
0
0
8
21
9
10
II
0
0
0
27
49
6
0
9 (75.0)
33 (97.0)
11 (91.7)
9 (100)
13 (100)
30 (100)
2 (100)
0
19 (73.0)
38 (92.7)
13 (100)
17 (100)
NS
NS
NS
NS
.024 (17.6; 0.9-343)
NS
NS
NS
NS
NS
NS
NS
Liver
Brain
Kidney
Epidural space
41
42
34
30
4 (9.7)
4 (9.5)
4 (\1.8)
0
2 (50.0)
4 (100)
I (25.0)
0
31
38
24
29
NS
NS
.048 (12.0; 1.05- 136)
NS
Liver
Brain
Kidney
Epidural space
41
42
34
30
19 (46.3)
33 (78.6)
11 (32.3)
26 (86.7)
14 (73.7)
33 (100)
7 (63.6)
26 (100)
19 (86.3)
9 (100)
18 (78.2)
3 (75)
NS
NS
NS
NS
Liver
Brain
Kidney
Epidural space
Liver
Brain
Kidney
Epidural space
41
42
34
30
41
42
34
30
13 (31.7)
4 (9.5)
25 (73.5)
4 (13.3)
11 (26.8)
8 (19.0)
0
0
9 (69.2)
4 (100)
18 (72.0)
3 (75)
10 (90.9)
8 (100)
0
0
24
38
7
26
23
34
25
29
NS
NS
NS
NS
NS
NS
NS
NS
Pain
Organ dysfunction
Duration of symptoms,
~14 d
Size of abscess,
~5
em
Multiple abscesses
Isolates
>1
Aerobic gram-positive
coccus
Aerobic gramnegative bacillus
Anaerobe
NOTE.
0
29 (52.7)
53 (56.3)
6 (31.6)
0
(72.7)
(95.4)
(100)
(100)
(61.1)
(93.\)
(92.5)
(100)
(83.8)
(100)
(80.0)
(96.7)
(85.7)
(100)
(77.7)
(100)
(76.7)
(100)
(73.5)
(96.7)
P values were determined with a two-tailed Fisher's exact test.
drainage. There have been no reports on prospective trials that
help determine the likelihood that a patient with a bacterial
abscess will respond to medical management. Therefore, it is
helpful to review the literature, but the information gained must
be weighed against possible biases.
Although the success rate was 85.8% in this report, it is
likely that there was considerable reporting bias. In the 1970s,
before the initial reports of successful medical management, it
is likely that failures of medical management were not reported
in the literature. Similarly, since there have been several reports
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Feature
Analyzed for
presence of
feature
em
Bamberger
596
Table 4.
1996;23 (September)
Radiographic procedures indicative of the presence of abscess(es), according to type of organ involvement.
No. of abscesses diagnosed by indicated procedure
Organ or site involved
CT
Ultrasonography
Nuclear
medicine
scan of
organ
Liver
Brain
Kidney
Epidural space
Subperiosteum of orbit
Spleen
Pancreas
Heart or heart valves
Seminal vesicle
17
103
7
20
19
3
6
0
1
12
3
19
0
1
14
3
4
0
17
9
4
3
0
5
0
0
0
Gallium
scan
Angiography
MRI
Other
Not
specified
5
0
7
3
0
1
0
1
0
0
1
13
0
0
0
0
0
0
0
1
0
8
0
0
0
0
0
1*
0
20 t
8t
0
0
0
0
0
141
35
20
13
0
0
0
0
0
t
Intravenous pyelography.
Myelography.
Table 5. Organisms isolated from the 169 patients whose abscess specimens were culture-positive.
No. of patients with indicated abscesses (n) whose cultures yielded organism
Organism isolated
Aerobic gram-positive
S. aureus
Viridans streptococci
Group A streptococci
Group B streptococci
Other streptococci
Enterococci
Listeria monocytogenes
Other
Aerobic gram-negative
E. coli
Klebsiella pneumoniae
Salmonella species
Proteus mirabilis
Pseudomonas aeruginosa
Yersinia species
Other
Anaerobic
Bacteroidesfragilis group
Bacteroides species
Fusobacterium species
Peptostreptococci
Prevotella species
Other
NOTE.
Total
(n = 170)
Liver
(n = 42)
Brain
(n = 42)
Kidney
(n = 32)
Epidural
space
(n = 30)
Spleen
(n = 11)
Pancreas
(n = 3)
Heart or heart
valve
(n = 5)
58
20
1
2
9
1
16
9
0
0
3
0
2
5
7
0
0
4
0
1
0
2
11
0
0
0
0
0
0
0
22
3
0
1
0
0
0
0
1
0
0
0
2
1
0
0
0
0
0
0
0
0
0
0
3
1
0
1
0
0
0
0
26
9
9
5
2
2
9
6
5
0
0
0
2
3
0
0
0
2
0
0
2
17
2
1
2
2
0
2
2
0
0
1
0
0
1
0
0
8
0
0
0
0
0
2
1
0
0
0
0
0
0
0
0
0
0
0
6
3
7
4
4
3
5
1
4
3
3
0
1
2
3
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
5
4
In addition, one seminal-vesicle abscess was due to E. coli and one abscess of the subperiosteum of the orbit was due to group A streptococci.
of series of successfully treated cases in the 1990s, it is likely
without therapeutic drainage, but the overall likelihood of sue-
that small numbers of successfully treated cases will no longer
cess remains less clear.
be reported. In addition, some clinicians may be less willing
Another potential concern is that some cases included in this
to report unsuccessfully treated cases. Therefore, it is known
review did not represent bacterial abscesses. Abscess formation
that a large number of cases have been successfully treated
is at the end of a continuum initiated with inflammation and
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* Gas evident on plain-film radiograph.
t
em 1996;23 (September)
Table 6.
597
Treatment of Abscesses Without Drainage
Number of patients with abscesses successfully treated, classified according to organ involvement, antimicrobial usage, and organisms
isolated.
No. of patients whose successfully treated abscess involved indicated site
Antimicrobial: total successes,
and successes against indicated
pathogen(s)*
Subperiosteum
of orbit
Spleen
Pancreas
Heart
16
2
9
0
1
8
6
1
0
0
0
5
2
1
6
0
0
0
0
0
2
2
0
0
0
0
0
0
0
3
2
3
4
2
0
0
I
0
0
0
0
0
0
0
Brain
Kidney
18
5
2
2
1
19
9
1
10
13
9
0
1
3
2
2
0
0
11
3
1
0
0
0
0
0
0
0
0
0
0
0
I
0
0
11
4
4
16
8
2
15
I
9
7
5
1
0
0
5
1
1
0
0
0
10
2
0
3
2
5
3
0
0
0
3
4
0
2
2
0
0
1
2
0
0
0
0
0
0
0
0
0
0
0
5
5
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
2
2
0
0
0
0
0
0
7
0
0
2
0
0
1
1
0
0
0
0
0
0
0
2
1
0
0
0
0
0
0
0
0
0
0
2
0
0
0
0
0
0
0
* The microbial etiology was not known in all cases; in addition, one patient with a seminal vesicle abscess was successfully treated with a ,B-Iactam plus an
aminog1ycoside.
leading to suppuration with capsule formation. Intermediate
stages may involve infected phlegmonous tissue with neither
frank suppuration nor a fibrous capsule. The diagnosis of abscess was made by the authors of the individual reports on the
basis of clinical, radiographic, and microbiological features.
Since in most cases material was not available for pathological
examination, it may have been difficult for the authors to distinguish bacteria-induced inflammation from an abscess.
It is likely that some of the reports included cases that did
not reach the stage of suppuration with fibrous capsule formation, since there are no clinical or radiographic modalities that
can reliably distinguish infected tissue from a frank suppurative
abscess with capsule formation. Most of the reports were from
the era after CT scanning became available, and a CT scan
demonstrating an abscess was the most commonly used diagnostic modality.
It is possible that ring enhancement observed on CT scanning
is due to inflammation without abscess formation (143].
Enzmann et al. [144] utilized delayed CT scanning in an attempt to distinguish cerebritis from abscess formation. In patients with cerebritis the magnitude of enhancement remains
unchanged for up to 60 minutes, whereas in patients with abscesses the enhancement fades. However, the fade in the enhancement in cases of abscess was not statistically significant
in comparison with baseline values, and of the eight patients
studied, five would not have been included in this report because their infections were due to higher bacteria, mycobacteria, fungi, or parasites.
Only a minority of patients had microbiologically proven
infections, a circumstance that raises the possibility that some
of the cases included did not represent bacterial infections. A
majority (84.3%) of the cases lacking microbiological documentation of infection (because either cultures were negative
or no information was provided) responded to antimicrobial
therapy, a value similar to the 88.2% success rate observed in
the cases in which the infection was microbiologically proven.
Downloaded from http://cid.oxfordjournals.org/ by guest on September 9, 2014
Aminoglycoside:
Total
Single gram + aerobe
Single gram - aerobe
Single anaerobe
Mixed
,B-Lactam drug alone:
Total
Single gram + aerobe
Single gram- aerobe
Single anaerobe
Mixed
,B-Lactam plus aminoglycoside:
Total
Single gram + aerobe
Single gram-aerobe
Single anaerobe
Mixed
Rifampin:
Total
Single gram + aerobe
Single gram - aerobe
Single anaerobe
Mixed
Metronidazole:
Total
Single gram + aerobe
Single gram - aerobe
Single anaerobe
Mixed
Epidural
space
Liver
598
Table 7.
Reference
em
Bamberger
1996;23 (September)
Failures of medical therapy in cases for which the type of antimicrobial therapy was known.
Site of
abscess
Liver
Liver
Liver
[88]
Liver
[88]
Liver
[88]
Liver
[88]
Liver
[101]
Liver
[121]
Kidney
[64]
Spleen
[64]
Spleen
[71]
E. coli
Klebsiella species
Streptococcus
species
Streptococcus
species
Streptococcus
species
S. aureus
E. coli, Klebsiella
species
E. coli, B. fragilis,
microaerophilic
streptococci
S. aureus
Antimicrobial(s)
administered
Duration
(d)
Abscess size
(largest, em)
28
42
14
10
3
Cm, Cthn
Pen, Gm, Mtz
Gm, Cthn
Gm, Amp
Comorbidity
Indication of
treatment
13
None
None
None
No response
No response
No response
3
10
None
No response
Cthn
7
6
None
No response
Naf
4
8
No response
Gm
7
6
PapillonLefevre
syndrome
None
Cm, Pen, Gm
9
5
None
No response
Amp, Amik
9
NS
None
No response
Pen, Gm
NS
NS
Endocarditis
Amp, Gm
NS
NS
Endocarditis
Death
Brain
Group D
streptococci
Enterococcus
faecalis
Unknown
Condition improved,
then worsened
Death
Amp, ChI
11
NS
None
[109]
Brain
Unknown
Amp, TMP-SMZ
4
NS
None
[4]
Brain
Unknown
Amp, Sulb
26
NS
[110]
Subperiosteal
orbit
Unknown
Naf, ChI
8
NS
Congestive heart
failure
None
Increase in abscess
size
Rise in intracranial
pressure; death
Died of congestive
heart failure
Increase in abscess
size
NOTE. Amik = amikacin; Amp = ampicillin; ChI = chloramphenicol; Cm = clindamycin; Cthn = cephalothin; Gm
Naf = nafcillin; NS = not stated; Pen = penicillin; Sulb = sulbactam; TMP-SMZ = trimethoprim-sulfamethoxazole.
Including only cases of microbiologically proven infection
would have been misleading because only a minority ofpatients
had positive blood cultures, and aspirations to prove infection
were often done only at the time of a drainage procedure because of antimicrobial failure.
The abscesses most commonly treated with medical therapy
and without therapeutic drainage involved either the liver or
the brain. Heineman et al. suggested in 1971 that brain abscesses may respond to medical therapy [58]. Between 1975
and 1985, 67 cases of brain abscess treated without surgery
were reported [145]. Although controversy exists [145], some
investigators have concluded that medical management should
be the treatment of choice for multiple abscesses if they are
small and if there is no associated major mass effect.
The first case-series report describing the treatment of liver
abscesses with medical management alone was by Maher et
al. in 1979 [82]. Although it is still controversial, medical
management has been suggested as a primary mode of therapy
for patients, unless celiotomy is needed for biliary tract disease
or to correct an intraabdominal process [146]. Diagnostic per-
= gentamicin; Mtz = metronidazole;
cutaneous aspiration may be needed to confirm the diagnosis
and to help guide the selection of antimicrobial agents.
Only a small number of heart or heart valve [53, 75, 115,
129], pancreatic [33, 45], or seminal vesicle abscesses [68]
were reported. The patients with heart or heart valve infections
typically had concomitant endocarditis, and the usual diagnostic modality was echocardiography. Five of the six pancreatic
abscesses were reported by one author. Recommendations for
these types of abscesses, based on this small number of cases,
remain speculative.
With the possible exception of one case involving a patient
with concomitant hepatic abscesses [99], all identified cases of
intraabdominal abscess involved the liver, spleen, kidney, or
pancreas. This suggests that at this time, nonvisceral intraabdominal abscesses are unlikely to respond to medical therapy
without drainage. In addition, no cases were found in which
medical management of psoas, paraspinous, or intervertebral
abscesses was attempted.
In the literature survey, all abscesses <5 em in diameter
responded to antimicrobial treatment without therapeutic drain-
Downloaded from http://cid.oxfordjournals.org/ by guest on September 9, 2014
[88]
[88]
[88]
Infecting
organism(s)
em
1996;23 (September)
Treatment of Abscesses Without Drainage
Older cephalosporins have been less reliable, but among the
newer cephalosporins, moxalactam [153], cefotaxime [154],
and ceftazidime [155] have all been found in adequate concentrations in brain abscesses. Aminoglycosides penetrate brain
abscesses poorly [152]. In a single case report, the vancomycin
concentration in a brain abscess was 18 j..tg/mL [156].
Experimental models have demonstrated well that most antimicrobial agents freely diffuse into abscesses despite the lack
of a vascular supply and the presence of a collagen wall [157].
However, the antibiotics may be deactivated by /3-lactamaseproducing organisms [157]. Among the /3-lactam drugs, those
that are more resistant to inactivation by /3-lactamases may
concentrate better in abscesses [157, 158).
Although it is likely that antimicrobial concentrations may
exceed the MICs for the involved pathogens, there are multiple
reasons why antimicrobials may fail to eradicate organisms in
an abscess milieu [159]. The low pH, ionic composition, and
low oxygen concentration may be inhibitory to antimicrobial
activity. Compared with their activity against growth-phase
organisms, many antimicrobials-including most /3-lactam
drugs-have less activity against the stationary-phase organisms present in a chronic abscess.
Eagle, in 1952, noted that when treatment is delayed for 24
hours, penicillin has less activity in a streptococcal myositis
infection model [160]. However, he also noted that when treatment is continued for several days, a cure can be achieved.
Aminoglycoside activity may be diminished by avid binding to
pus sediment [1]. Sequestration of organisms inside neutrophils
may limit the activity of antimicrobials that have little intracellular penetration or activity [161]. Neutrophil proteins such as
calprotectin may inhibit but not kill bacteria and render them
less susceptible to the bactericidal effects of antibiotics [162,
163].
In experimental models, some antimicrobial regimens have
produced better results in an abscess milieu than others, and
these results could not have been predicted on the basis of
standard in vitro testing. Metronidazole is more rapidly bactericidal than other agents in a B. fragilis subcutaneous abscess
model [164). Ciprofloxacin plus rifampin is more effective in
an E. coli model [165] and significantly more effective in an
S. aureus model [166], as compared with the effectiveness
of ciprofloxacin alone. The combination of cefotaxime and
amikacin is significantly more effective than either agent alone
in an E. coli model [159].
This literature-review study showed that only 11 patients'
therapy failed, among cases in which both the microbiological
data and antimicrobial-use data were provided. Seven of these
patients were described in the same report [88]. In that report
of patients with liver abscesses [88], it was noted that the abscess
tended to be large, none of the abscesses yielded anaerobes (a
finding suggesting that appropriate anaerobic cultures were not
performed), and aminoglycosides were frequently used without
documentation of adequate therapeutic concentrations.
This review also revealed that treatment failed for four of
eight patients who received an aminoglycoside as the only
Downloaded from http://cid.oxfordjournals.org/ by guest on September 9, 2014
age; 74.1% of abscesses ~5 em in diameter also responded to
medical management. Although investigators have commented
that abscess size may influence outcome [145, 146], only in
cases of tubo-ovarian abscess has abscess size been demonstrated to influence outcome [147].
Animal model data have suggested that the encapsulation
phase of abscess formation does not begin until 10 days after
infection, and is not complete until 14 days after infection
[148]. It was postulated that as a result, the outcome for patients
presenting earlier in the course of infection- perhaps before
the phase of frank: suppuration with encapsulation-may be
better. Among the patients in this report, no difference could
be found in the outcomes for those treated within 14 days of
the onset of symptoms vs. the outcomes for those treated after
14 days. It is still possible, however, that the stage of abscess
formation may influence outcome and that the duration of clinical symptoms correlates poorly with the degree of suppuration
and encapsulation.
The organisms reported in table 5 are typical of the organisms seen in most cases of abscesses of the liver, brain, kidney,
epidural space, heart or heart valves, and pancreas. Only in the
cases of splenic abscess, in which eight of 11 patients had
infections due to Salmonella species, was a typical microbiological pattern not observed. This raises the likelihood that
splenic abscesses due to Salmonella species may be easier to
treat with medical management than splenic abscesses due to
other organisms.
The use of prior antimicrobial therapy could not be ascertained from the majority of reports; thus, the influence of prior
antimicrobial therapy on the type of organisms recovered at
the time of aspiration could not be analyzed. It is possible that
prior antimicrobial therapy influenced the rate of recovery of
organisms and the type of organisms reported in table 5.
In addition to abscess size, the other clinical variables that
predicted a decreased likelihood of success were the isolation
of more than one organism and the presence of gram-negative
aerobic bacteria. No other reports have made this association.
Among anaerobic bacteria, Bacteroides fragilis is highly associated with intraabdominal abscess formation, perhaps secondary to its capsular polysaccharide through mediation with
T lymphocytes [149]. Of the six cases involving abscesses due
to the B. fragilis group, medical management failed in only
one.
Failure of antimicrobial therapy for abscesses may be related
to either inadequate antimicrobial concentrations within the
abscess or inadequate antimicrobial activity within the abscess
milieu. With the exception of the brain, prostate, and aqueous
humor, antibiotics penetrate most body tissues [150]. Although
there is experimental evidence that the blood-brain barrier is
not equivalent to the blood-CSF barrier [151], most antimicrobials that penetrate the blood-CSF barrier well (such as chloramphenicol, metronidazole, sulfonamides, and rifampin) also
enter into brain tissue.
With regard to /3-lactam drugs, most studies have shown
adequate concentrations of penicillin in brain abscesses [152].
599
600
Bamberger
Acknowledgments
The author thanks Betty L. Herndon, Jill Moormeicr, Jean
Sarkis, and Michelle Dew for assistance in data collection and
analysis.
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