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Title Retrospective review of clinical presentations, microbiology andoutcome of psoas abscess in a regional hospital

Author(s) Wong, Oi-fung; žÃ ñ ï

Citation

Issued Date 2012

URL http://hdl.handle.net/10722/173734

Rights Creative Commons: Attribution 3.0 Hong Kong License

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Retrospective review of clinical presentations, microbiology and outcomeof psoas abscess in a regional hospital

By

Dr. Wong Oi Fung

This work is submitted to

Faculty of Medicine of The University of Hong Kong

In partial fulfillment of the requirements for

The Postgraduate Diploma in Infectious Diseases, PDipID (HK)

Date: 09/01/2012

Supervisor: Dr. Ho Pak Leung

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Abstract

Background: The clinical features of psoas abscess in local setting, including the

microbial causes, the prevalence and etiologies of secondary psoas abscess, have not

been well described.

Objective: To review the clinical features and outcome of patients with psoas

abscess in a regional hospital

Method: A retrospective study was conducted. Patients with psoas abscess who

were admitted into Tuen Mun Hospital from 1 st January 2006 and 31 st December

2010 were included. The clinical presentations, etiologies, microbiology, treatment,

hospital stay, ICU admission and outcome were reviewed.

Results: Forty-two cases were included. Five cases developed psoas abscess after

admission. The average age was 60.9 ± 16.4 years (ranged 27 to 96 years). Twelve

of them had diabetes mellitus and seven of them were intravenous drug abusers. The

most common presenting symptoms were back, hip or thigh pain (43% [16/37]).

Fever was present on presentation in 41% (15/37) of cases and four patients

presented with fever only. Diagnosis was made by computerized tomography scan in

95.2% (40/42) of all the cases. Twenty-three cases were considered to be secondary

and the most common etiology was infective spondylitis or spondylodiscitis. The

most causative organism of primary psoas abscess was Staphylococcus aureus while

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secondary psoas abscesses were more commonly caused by organisms from

gastrointestinal and genitourinary tracts. There was no statistical difference in the

proportions of cases with bacteremia (p=0.404) between primary and secondary

psoas abscess. Primary psoas abscess appeared to be associated with higher

mortality but not to the extent of statistical significance (26.3% [5/19] Vs 4.3%

[1/23]; p=0.075) while secondary psoas abscess had longer length of hospital stay

(mean 62.1 days Vs 34 days; p=0.007). Half of the cases were treated with CT

guided drainage and six cases were treated conservatively. Others were treated with

ultrasound guided or surgical drainage. The overall in-hospital mortality rate was

14.3% (6/42). There was no significant difference in the mortality regardless of the

causative organisms, the presence of bacteremia and background of diabetes mellitus.

Elderly patients (more than 70) appeared to have higher mortality (66.7% [4/6]Vs

25% [9/36]; p=0.063). Mortality was not shown to be related to the delay in making

diagnosis.

Conclusion: Psoas abscess is an uncommon condition. Most patients presented with

only nonspecific symptoms leading to the difficulty in making an early diagnosis. A

larger proportion of secondary psoas abscess was encountered and the etiology

profile was different from oversea experiences.

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Introduction

Psoas abscess is an uncommon but dangerous condition. The high susceptibility of

the psoas muscle for infections is related to its unique anatomy. Infections could be

caused by either direct extension or distal seeding. The psoas muscle originates from

the lower thoracic to the entire lumbar vertebrae (lateral borders of T12 to L5

vertebrae), continues through the pelvic retroperitoneum and over the pelvic brim to

insert on the lesser trochanter of femur. It lies in close proximity to a number of

retro- and intra-abdominal organs including kidneys, ureters, pancreas, appendix,

and large and small intestines. Infections from these organs could spread directly to

the psoas muscle. The abundant blood supply of the muscle is believed to be a

predisposing factor for haematogenous spread of infections from distant sources. 1

The clinical presentation is usually insidious. The classical clinical triad, fever, back

pain, and flank or groin mass, only presents in minority of patients. Treatment

consists of adequate drainage either percutaneously or surgically with prompt

antibiotic therapy. Serious complications such as sepsis and even mortality could

result from delay in diagnosis. Presence of co-morbidities is also associated with

poor prognosis. Psoas abscess is traditionally classified into primary or secondary

depending on the presence or absence of an identifiable infectious focus in the

adjacent structure. Previous studied showed high prevalence of primary psoas

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abscess in Asia. 2 In 1966, Lam et al published a local study involving twenty-four

patients with primary psoas abscess treated in Queen Elizabeth and Queen Mary

Hospitals between 1961 and 1965 but all the cases resulting from infections of

pelvic, retroperitoneal and thoracic organs were excluded. 3 Local prevalence of

primary and secondary psoas abscesses, the etiologies of secondary psoas abscess

and the microbial causes have not been well described.

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Material and methods

All clinical data was retrieved from hospital electronic record database, the Clinical

Data Analysis & Reporting System (CDARS), which is a computerized data

retrieval system of the Hospital Authority of Hong Kong. 4 The diagnosis of psoas

abscess (ICD-9 coding 728.89) under the categories of “any diagnoses” was

searched. Patients with psoas abscess admitted into Tuen Mun Hospital between the

period of 1 st January 2006 and 31 st December 2010 were included. The inclusion

criteria are: (1) The diagnosis of psoas abscess was established by either imaging,

including computerized tomography (CT) or magnetic resonance imaging (MRI), or

surgical drainage, (2) Patients were more than 18 years old, and (3) Complete

clinical records were available for review. Patients were excluded if the diagnosis

was made only based on clinical suspicion without radiological or operative

confirmation. Clinical presentations, including symptoms, signs and duration,

microbiology, underlying pathologies, treatment and outcome were reviewed from

the clinical records. The study was approved by the cluster ethics committee.

Statistical analyses

The Statistical Package for Social Sciences (SPSS) version 19.0 for Windows was

used for analysis. Descriptive statistics were used to summarize patient demographics

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data. The Student’s t test was used to compare continuous variables between the two

groups, while the Chi square test and Fisher's Exact Test were used to compare

categorical variables. A p-value of less than 0.05 was considered statistically

significant.

Definitions

Psoas abscess is classified into primary or secondary, depending on the presence or

absence of underlying diseases. Primary psoas abscess is defined as psoas abscess

without an identifiable source of infection outside the psoas abscess while secondary

psoas abscess is defined by the presence of a contiguous infectious focus in the

adjacent structures (e.g. infections involving adjacent vertebra, intestine, kidney and

abdominal aorta). 1 Sepsis is defined according to the definition by the American

College of Chest Physicians/Society of Critical Care Medicine Consensus

Conference. 5

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Results

Fifty cases of psoas abscess were identified during the study period. Eight cases

were excluded. Four cases with history of psoas abscess had wrong diagnosis coding

of psoas abscess and the reasons for the episode of admission were not related to

psoas abscess. One patient of age 17 was suffering from acute myeloid leukaemia

and was clinically admitted for chemotherapy. The patient eventually died of

uncontrolled sepsis with intra-abdominal fungal infection and psoas abscess. One

case was admitted for suspected psoas abscess but the patient was eventually

discharged with the acknowledgment of medical advice before the confirmatory

investigation. Another patient with history of psoas muscle collection due to

previous pancreatitis and drainage was admitted for damaged drainage catheter. One

patient, who had been already included in the study, was readmitted because of

drainage wound infection. (Figure 1)

Patient characteristics

The mean age of patients was 60.9 ± 16.4 years (ranged 27 to 96 years). Twenty

seven cases were male and fifteen cases were female. Five patients enjoyed good

past health. Seven patients were intravenous (IV) drug abusers and three of them did

not have significant medical illnesses. Others had at least one medical illness,

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including diabetes mellitus (DM), hypertension (HT), ischemic heart disease,

chronic obstructive airway disease, cerebral vascular accident, dementia,

parkinsonism, renal failure, chronic hepatitis infections, and so on. Among them,

twelve had DM. Six patients had underlying malignancy (hepatocellular carcinoma,

Ca sigmoid/colon, Ca cervix and Ca prostate). None of them had liver cirrhosis and

underlying hematological malignancy. One patient had long term steroid therapy for

rheumatic arthritis and one patient was on chemotherapy for Ca colon.

Clinical presentations

Five cases developed psoas abscess after admission and the presenting symptoms or

admission reason were unrelated to the psoas abscess. The details of these five cases

are summarized in table 1 while the clinical presentations on admission of the

remaining thirty-seven cases are summarized in table 2. Among these thirty-seven

cases of community-onset psoas abscess, eighteen cases (including four patients

transferred from Poh Oi Hospital) were initially admitted into the medical unit,

thirteen cases into the orthopedic unit and five cases into the surgical unit. One

patient was directly admitted into intensive care unit (ICU) for the management of

septic shock. Around half of the patients (43.3% [16/37]) presented with back, hip or

thigh pain and 13.5% (5/37) of patients presented with abdominal pain. Fever was

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present in 40.5% (15/37) of patients and four patients had initial presentation of

fever only. Groin or back mass and limited hip movement were detected in around

one third and one fifth of the cases respectively. No patients presented with the

classical triad (fever, back pain, and groin or frank mass) and had documented

abnormality of the psoas muscle shadow in the radiographic imaging on admission.

There was evidence of sepsis in 43.2% (16/37) of the patients and 8.1% (3/37) of the

cases had hypotension on presentation. Four patients presented with decreased

general condition and two patients who presented with shortness of breath were

admitted into medical ward for suspected chest infection. One patient presented with

coffee ground vomiting and poor DM control and one patient with mycotic

aneurysm of the left internal iliac artery secondary to salmonella septicemia

presented with left lower limb deep vein thrombosis due to the extrinsic

compression on the left iliac vein.

Diagnosis

The diagnoses of psoas abscess in 95.2% (40/42) of the cases were made by CT scan.

Psoas abscess was confirmed by MRI in one patient and the other one patient had

psoas abscess diagnosed intraoperatively. Bilateral psoas abscesses were detected in

eight cases and thirty-four cases had unilateral psoas abscess (right-sided psoas

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and sixteen patients respectively. Methicillin-sensitive Staphylococcus aureus

(MSSA) was the most common organism isolated in both blood and pus cultures. It

was also the most common causative organism for primary posas abscesses (37.5%

[6/16]; three patients did not have pus cultures performed). Methicillin-resistant

Staphylococcus aureus (MRSA) was isolated in both pus and blood cultures in two

cases. One patient enjoyed good past health without recent hospitalization or

medical procedure and the other patient with multiple medical illnesses had been

recently hospitalized. In contrast to primary psoas abscesses, secondary psoas

abscesses were more commonly caused by organisms from GI or genitourinary(GU)

tracts (30% [6/20]; three cases of secondary psoas abscess did not have pus cultures

performed) including Bacteroids species, E. coli, Klebsiella and group B

Streptococcus (Streptococcus agalactiae).

Psoas abscesses due to tuberculosis (TB) infection

There were six cases of psoas abscess due to TB infection with average age of 54

years (ranged from 32 to 96). All, except one patient, were admitted from the

emergency department. The other patient had history of TB psoas abscess and was

found to have recurrent psoas abscess during follow-up. This patient was then

admitted clinically for surgical drainage. Four of the six cases them presented with

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groin or flank mass. Only two patients had fever on presentation. The pus or wound

swab cultures were negative for other bacteria in all of the cases. The initial Acid

fast bacillus smear was positive in only one patient. One patient had positive sputum

culture for TB and another one had TB found in gastric lavage. Two cases out of six

were considered to primary and other four cases were secondary to infections

involving spine or pelvis including infective spondylitis/spondylodiscitis,

osteomyelitis of vertebral bodies and osteomyelitis of hip. The mortality rate of TB

psoas abscess was 16.7% (1/6).

Psoas abscess in IV drug abusers

Seven patients were IV drug abusers. Six of them were considered to be primary and

the other one had psoas abscess secondary to left hip septic arthritis. Pus cultures

were positive for Staphylococcus aureus in six of them including the patient with

secondary psoas abscess. One patient had Streptococcus milleri and Prevotella

intermedia found in the pus. Among the six patients with Staphyloccocus aureus

infections, five of them had single bacterial growth in the pus cultures and one

patient had mixed growth with Staphylococcus aureus, Pseudomonas aeruginosa,

and Peptostreptococcus species. All patients with positive pus cultures of

Staphyloococcus aureus also had Staphylococcus aureus bacteremia. No

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MRSAinfection was recorded.

Treatment and Outcome

Around half of the patients (54.8% [23/42]) were treated with CT guided drainages.

Four patients underwent ultrasound guided drainage and ten patients had surgical

drainages performed. The mean length of hospital stay was 49.4 days (ranged from 8

to 183 days). Six cases (14.3%) required ICU admission. The overall in-hospital

mortality rate was 14.3% (6/42). One patient was complicated with deep vein

thrombosis and developed sudden cardiac arrest during the hospital stay. Two

patients died of uncontrolled sepsis. One patient with poor pre-morbid status was

treated conservatively after discussion with patient’s family. One patient died of

multi-drug resistant Acinetobacter infection and another patient with terminal

malignancy died of disseminated TB infection. There was no significant difference

in the mortality regardless of the causative organisms, the presence of bacteremia,

and background of DM. Mortality was also not shown to be related to the delay in

making diagnosis. However, there was a trend of increased mortality in elderly

patients (more 70 years) (66.7% Vs 25%; p=0.063). (table 6)

Initiation of antibiotics in patients initially presenting with musculoskeletal

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symptoms

Thirteen patients were admitted into orthopedic units and the diagnoses of psoas

abscess in two of them were made by the private CT/MRI before admission. Among

the eleven patients with psoas abscesses diagnosed after admission, only three

patients had fever on presentation. Antibiotics were started before the confirmatory

investigation in half of the patients with the diagnosis made after admission. The

reasons for the initiation of antibiotics included suspicion of infectious foci (e.g.

septic arthritis of hip and septic spondylitis) in two patients and confirmed

bacteremia in another three patients.

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Discussion

In 1986, Rocci et al. reviewed 367 cases of psoas abscess from the world literature

and reported a difference in the etiology world wide. 70% (200 out of 286 cases) of

primary psoas abscess occurred mainly in the developing countries while secondary

abscesses appeared exclusively in reports from developed countries including

Europe, the United States and Canada. The most commonly reported etiology for

secondary abscess was Crohn’s disease. More recent studies also revealed Crohn’s

disease as the most common etiology of secondary psoas abscess in oversea

countries. 6, 7 Secondary psoas abscess was reported to be more likely to occur in

older patients. 2 However, this observation was not found in this study.

Primary psoas abscess occurs probably as a result of the hematogenous seeding from

an infectious process in a distant occult source. Other proposed pathogeneses

include suppurative lymphadenitis, and trauma with haematoma formation and

secondary infection. 8, 9 Medical conditions causing immunosuppression (including

DM, human immunodeficiency virus infection, on steroid or chemotherapy) are risk

factors for primary psoas abscess. 1 Secondary psoas abscess is caused by the spread

from an adjacent infectious process. In contrast to data from oversea studies,

spondylitis (spondylodiscitis with disc involvement) was found to be the most

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common etiology of secondary psoas abscess in this study and no cases were

reported to be related to Crohn’s disease. Spondylitis is an infrequently encountered

condition and is the main manifestation of haematologenous osteomyelitis in

middle-aged patients (over 50). Staphylococcus aureus has been reported to be the

most predominant pathology pathogen 10 and was found to be the causative organism

in two cases of psoas abscess secondary to spondylitis or spondylodiscitis in this

study (TB in two cases, E. coli in one case and negative growth in another four

cases). Pyogenic sacroiliitis 11, infection of kidney 12 and aortic infection 13 are

uncommon etiologies of psoas abscess. Predisposing factors of pyogenic sacroiliitis

include IV drug abuse and trauma. Like spondylitis, Staphylococcus aureus is also

the most common causative organism for pyogenic sacroiliitis. 14 Group B

streptococcus (Streptococcus agalactiae) is an important pathogen causing neonatal

meningitis and sepsis, Cases of sacroiliitis due to group B Streptococcus infections

were rarely reported. 15 Mycotic aneurysm is a rare but potentially life-threatening

condition. Most of reported cases of psoas abscess related to aortic infection were

caused by Salmonella infection. 13 Transient bacteremia occurs in less than 10% of

patients with non-typhoid salmonella infection. 16 Salmonella bacteraemia, which

particularly infects structurally abnormal vasculatures as in atherosclerosis, causes

necrosis of the intima and preexisting aneurysm. Elderly patients are therefore

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References

1. Mallick IH, Thoufeeq MH, Rajendran TP. Iliopsoas abscesses. Postgrad Med J.

2004;80(946):459-62.

2. Ricci MA, Rose FB, Meyer KK. Pyogenic psoas abscess: worldwide variations

in etiology. World J Surg. 1986;10(5):834-43.

3. Lam SF, Hodgson AR. Nonspinal pyogenic psoas abscess. J Bone Joint Surg. J

Bone Joint Surg. 1966;48A(5):867-877.

4. Clinical Data Analysis and Reporting System, Hospital Authority, Hong Kong.

(Accessed 17 Oct 20011.)

5. American College of Chest Physicians/Society of Critical Care Medicine

Consensus Conference: definitions for sepsis and organ failure and guidelines

for the use of innovative therapies in sepsis. Crit Care Med. 1992;20(6):864-74.

6. . Procaccino JA, Lavery IC, Fazio VW, Oakley JR. Psoas abscess: difficulties

encountered. Dis Colon Rectum. 1991;34(9):784-9.

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13. Inufusa A, Mikawa Y, Morita I, Fujiwara T. Ruptured abdominal aortic aneurysm

associated with a psoas abscess. Arch Orthop Trauma Surg. 2002

Jun;122(5):306-7.

14. Vyskocil JJ, McIlroy MA, Brennan TA, Wilson FM. Pyogenic infection of the

sacroiliac joint. Case reports and review of the literature. Medicine (Baltimore).

1991 ;70(3):188-97.

15. Corominas H, Domingo P, Llobet JM, Caballero F, Díaz C, Vázquez G. Group

B Streptococcal sacroiliitis: case report and review. Scand J Infect Dis.

2001;33(9):708-10.

16. Nielsen H, Gradel KO, Schønheyder HC. High incidence of intravascular focus

in nontyphoid Salmonella bacteremia in the age group above 50 years: a

population-based study. APMIS 2006;114(9):641-645.

17. Soravia-Dunand VA, Loo VG, Salit IE. Aortitis due to Salmonella: Report of 10

cases and comprehensive review of the literature. Clin Infect Dis

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1999;29(4):862-8.

18. Charalampopoulos A, Macheras A, Charalabopoulos A, Fotiadis C,

Charalabopoulos K. Iliopsoas abscesses: diagnostic, aetiologic and therapeutic

approach in five patients with a literature review. Scand J Gastroenterol.

2009;44(5):594-9.

19. Chern CH, Hu SC, Kao WF, Tsai J, Yen D, Lee CH. Psoas abscess: making an

early diagnosis in the ED. Am J Emerg Med. 1997;15(1):83-8.

20. Zissin R, Gayer G, Kots E, Werner M, Shapiro-Feinberg M, Hertz M. Iliopsoas

abscess: a report of 24 patients diagnosed by CT. Abdom Imaging.

2001;26(5):533-9.

21. Cantasdemir M, Kara B, Cebi D, Selcuk ND, Numan F. Computed

tomography-guided percutaneous catheter drainage of primary and secondary

iliopsoas abscesses. Clin Radiol. 2003;58(10):811-5.

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Figure 1. Profile of the study

50 records of psoas abscess were

identified by CDARS between 1st

January 2006 and 31 st December 2010

Inclusion criteria:

1. Diagnosis of psoas abscess wasestablished by either imaging (e.g.

CT or MRI), or surgical drainage2. Patient with age more than 18

years

3. Clinical records were completeand available for review

Exclusion criteria:

1. Diagnosis was made only basedon clinical suspicion without

radiological (CT and/or MRI) or

operative confirmation

42 cases were included. 5 cases

developed psoas abscess after

admission and the initial presentation

on admission was not related to psoas

abscess (table 1)

8 cases were excluded:

-Wrong diagnosis coding for the

episode of admission in 4 cases

-1 patient of age less than 18

-1 case with suspected psoas abscess

without confirmatory investigation

-1 case with known psoas muscle

collection due to pancreatitis

amitted for damaged drainage

catheter

-1 case with known psoas abscess

(already included in the study)admitted for infected drainage

wound

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Table 1. Cases of psoas abscess developed after admission

Age Sex Background Clinical course

77 F BPH, HT, old CVA Admitted for left knee septic arthritis with operation done. Developed

lower limbs weakness during hospital stay. CT/MRI of lumbar spine

showed infective spondylodiscitis of L4/L5 and bilateral psoas abscesses.

CT

76 F Depression, hepatitis B

and C carrier, Ca breast,

CVA, BCC of nasolabial

fold, HCC

Clinically admitted for radiofrequency ablation of HCC and complicated

with recurrent CVA. CT scan of abdomen performed for persistent fever

and showed psoas abscess

Co

be

ab

74 M DM, AF,

cholangiocarcinoma with

Whipple operation done

Admitted for biliary sepsis. CT scan showed liver abscess. Follow‐up CT

scan showed new psoas abscess and resolving liver abscess Fa

be

ab

m

66 M Advanced Ca sigmoid Palliative total colectomy with ileostomy done. Postoperatively found persistent pus discharge from abdominal drain. CT scan of abdomen

showed psoas abscess

CT

70 F DM, HT, CVA, Ca sigmoid

with liver metastasis Hartmann’s operation for Ca sigmoid with intestinal obstruction

performed. Leukocytosis and abdominal pain after operation. CT scan of

abdomen showed multiple retroperitoneal and intraperitoneal

abscesses

CT

BPH: benign prostate hyperplasia; HT: hypertension; CVA: cerebral vascular accident; BCC: basal cell carcinoma; HCC: hepato

diabetes mellitus, AF: atrial fibrillation

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Table 2. Summary of clinical presentations on admission for 37 cases of

community-onset psoas abscess

Clinical presentation No. (percentage)

Pain (total)

Abdominal pain

Back/hip/thigh pain

21 (57%)

5 (14%)

16 (43%)

Fever (Temperature > 38C o) 15 (41%)

Groin/frank mass 10 (27%)

Limited hip movement 8 (22%)

Sepsis 16 (43%)

Hypotension (systolic blood pressure

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Table 3. Etiologies of 42 cases of psoas abscess

Etiologies No.

Primary

Secondary

Total

Musculoskeletal

Infective spondylitis/ spondylodiscitis

Pyrogenic sacroiliaitis

Osteomyelitis of vertebral bodies

Septic arthritis of hip

GI

*Ca colon/ sigmoid

Peritoneal metastasis with infectionLiver abscess

GU

*Ca cervix

Ureteric stone with pyronephrosis

Vascular

Mycotic aneurysm secondary to Salmonella septicemia

Other

Suspected retained foreign body in psoas muscle

19

23

9

1

1

3

3

11

1

1

1

1*The cases were possibly related to infection of the tumors.

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Table 4. Comparison between primary and secondary psoas abscess (n=42)

Primary Secondary P value

Mean age (SD) 63.6 (17.3) 58.6 (16.1) 0.34*

Underlying medical illnesses

DM (no./%)

Underlying malignancy (no./%)

Long-term steroid use (no./%)

On chemotherapy (no./%)

7 (36.8%)

2 (10.5%)

0 (0%)

0 (0%)

6 (26.1%)

4 (17.4%)

1 (4.3%)

1 (4.3%)

0.453 ^

0.427 ^

0.358 ^

0.358 ^

Bed/chairbound (no./%) 3 (15.8%) 3 (13%) 1.00 ^

Bacteremia (no./%) 9 (52.9%) 7 (38.9%) 0.404**

ICU admission (no./%) 3 (15.8%) 3 (13%) 1.00 ^

Length of hospital stay (mean/SD)[days] 34 (17.1) 62.1 (39.8) ┼ 0.007*Mortality (no./%) 5 (26.3%) 1 (4.3%) 0.075 ^

total 19 23^ Fisher’s Exact test; **Chi-Square test; *Pair t-test; ┼ Statistically significant.

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Table 5. Microbiology results

Primary (n=19) Secondary (n=23)

Source of positive culture

Blood culture alone 1 2

Psoas abscess pus alone 6 9

Both 8 4

Negative culture 4# 8##

Subtotal 19 23

Microorganisms

Negative culture 2 7

No pus culture performed 3 3

Monomicrobial

MSSA 5 3

MRSA 2 0

TB 2 4

Others 3* 4^

Polymicrobial

2 organisms 1** 1^^

3 organisms 1*** 1^^^

>3 organisms 0 0

Subtotal 19 23

# 1 case had negative pus and blood cultures; 1 case had negative pus culture but no

blood culture was performed; 2 cases did not have pus culture done and blood cultures

were negative.

## 5 cases had negative cultures in both pus and blood; 2 cases had negative pus

culture but no blood cultures were performed; 1 case did not have pus culture done

and the blood culture was negative.*Proteus mirabilis, Klebsiella pneumoniae (x2)

**Streptococcus milleri + Prevotella intermedia

***Staphylococcus aureus + Pseudomonas aeruginosa + Peptostreptococcus species

^Bacteroides species, E. coli (x2), Streptococcus agalactiae (group B streptococcus)

^^Klebsiella + E.coli

^^^E.coli + Klebsiella +Alpha-hemolytic streptococcus

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Table 6. Analysis of mortality

Alive (no.) Death (no.) P value

Pus cultures

MSSA

MRSA

GI/GU bacteria

TB

Negative#T otal

7

2

9

5

10

33

2

0

0

1

0

3

0.316**

#Bacteremia 13/29 (44.8%) 3/6 (53%) 1.000 ^

Age >70 9/36 (25%) 4/6 (66.7%) 0.063 ^

DM 11/36 (30.6%) 2/6 (33.3%) 1.000 ^

##Delayed diagnosis>1 day after admission

>5 days after admission

22/31 (71.3%)

14/31 (45.2%)

6/6 (100%)

5/6 (83.3%)

0.302 ^

0.180 ^

** Chi-Square; ^Fisher Exact test; ┼ statistically significant.# Six cases did not have pus culture done and seven cases did not have blood culture

performed. ## Five cases with psoas abscess developed after admission are excluded.

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Figure 2. (a) CT scan showed multiple abscess involving abdominal wall (white

arrow head), right iliac (black arrow), right psoas (black arrow head) and right gluteal

muscles (white arrows). The right sacroiliac joint is eroded (curved black arrow). (b)

A mycotic aneurysm over the left internal iliac artery (white arrow) with a left psoas

abscess (white arrow head) is shown. (c) Right hydronephrosis (black arrow head) is

caused a distal ureteric stone (not shown in the figure). Peri-renal fat stranding (white

arrow) indicates inflammatory change. A large right psoas abscess with internal gas

locules is pointed by the curved white arrow. (d) Metallic density (small black arrow)

is found inside a right psoas abscess (large black arrow). Retained foreign body is

suspected.