BACTERIAL AETIOLOGY OF OSTEOMYELITIS CASES AT FOUR HOSPITALS OF LAHORE

Faria Malik

Department of Pathology, Fatima Jinnah Medical College, Lahore, Pakistan.

Background: The conclusive diagnosis of osteomyelitis requires isolation of pathogen in aspirate from bone lesion, bone debridement and blood culture. The present research was undertaken to study the microbiological pattern of cases of osteomyelitis reporting to four hospitals in Lahore. Method: One hundred and fifty patients of osteomyelitis were selected from outpatient departments and Orthopaedic wards of Lahore General Hospital, Sir Ganga Ram Hospital, Services Hospital and Mayo Hospital, Lahore. Specimens of pus from bone, blood and bone debridement were collected. All samples were inoculated onto two Blood Agar and one MacConkey agar plates. One Blood Agar plate was incubated anaerobically for 48 hours and the other two plates aerobically for 24 hours. Smears were made from samples and stained by the Gram’s stain. The colonies obtained were processed according to the technique of Mackie and MacCartney. Results: The commonest isolates belonged to the Enterobacteriaceae (32.8%), followed by Staphylococcus aureus (29.5%), Pseudomonas aeruginosa (15.5%), anaerobes (2.6%) and miscellaneous (19.3%). Five (2.7%) anerobic bacteria were isolated. Anaerobic bacteria were peptostreptococci, peptococci and bacteroides either alone or as a mixed infection. Conclusion: The present study highlights the importance of microbiological examination of bone in cases of osteomyelitis. Different types of bacteria either alone or as a mixed infection could be the causative agent(s).

Key Words: Bacteria, Aerobes, Staphylococci, Enterobacteriaceae, Pseudomonas, Anaerobes, Osteomyelitis.

INTRODUCTION

Infections of the bone have been known for a long time. Attempts at understanding the disease began a century ago, when in 1884 Rodet reported to the Academy of Sciences in Paris, his experimental production of haematogenous osteomyelitis in animals by means of intravenous injection of Staphylococci¹. The micrococci were injected into a rabbit which developed typical lesion of osteomyelitis in long bones².

The most common route by which bacteria reach the bone is blood stream^3,4. However, traumatic modes as penetrating injury⁵, fractures and intramedullary nailing⁶ and post-surgical complications⁷ have been identified. Intravenous drug users^8,9 and  foreign  body  presence¹⁰  also  predispose  to bone infection. The initial diagnosis of osteomyelitis is usually made on physical signs¹¹ and by sonography for early soft tissue changes^12,13. Magnetic resonance imaging¹⁴ and bone scans¹⁵ are most sensitive and specific. Conclusive diagnosis requires isolation of pathogen in aspirate from bone lesion, bone debridement and blood culture¹⁵.

In Pakistan, only a few workers have studied the bacteriological pattern of osteomyelitis. The reports from different cities have shown different bacteriological pattern. In a study at Karachi¹⁶, out of 125 cases, 68.6% were reported to be infected with Staphylococci. Karamat et al¹⁷ from Rawalpindi have also reported a high frequency (79%) of Staphylococci, whereas Farooq and Ahmad¹⁸ have reported a very low (37.5%) frequency of Staphylococci. Studies from  abroad by  Karwowska et al¹⁹ Alonge et al²⁰ and  Lobati et a1¹⁰  also support  the  predominant  role  of Stapyhlococci  in   bone  infection.

The present research study was undertaken to study the microbiological pattern of cases of osteomyelitis reporting to four hospitals in Lahore.

MATERIAL AND METHODS

The study was conducted at the Department of Microbiology, Postgraduate Medical Institute, Lahore. One hundred and fifty patients were selected from outpatient departments and Orthopaedic wards of Lahore General Hospital, Sir Ganga Ram Hospital, Services Hospital and Mayo Hospital, Lahore.

The patients included were from both sexes and all age groups. The only exclusion criterion was those patients who were on antibiotic therapy.

Specimens of pus from bone, blood and bone debridement were collected. All samples were inoculated onto two Blood Agar and one MacConkey agar plates. One Blood Agar plate was incubated anaerobically for 48 hours and the other two plates aerobically for 24 hours.

Smears were made from samples and stained by the Gram’s stain. The colonies obtained were processed according to the technique of Mackie and MacCartney²¹.

RESULTS

The age of the patients ranged from 2–90 years with a mean age (±SD) of 28.73±16.64 years. There were 105 males and 45 females.

There were four specimens of bone curetting, two specimens of blood and 144 specimens of pus. Out of these 150 specimens 186 isolates were identified.

The positivity rate according to various hospitals is shown in Table-1.

Table-1: Distribution of positive cultures according to the hospitals.

The commonest isolates belonged to the Enterobacteriaceae (32.8%), followed by Staphylococcus aureus (29.5%), Pseudomonas aeruginosa (15.5%), anaerobes (2.6%) and miscellaneous (19.3%).

The distribution of isolates according to various age groups is shown in Table-2. Five (2.7%) anaerobic bacteria were isolated. Anaerobic bacteria were peptostreptococci, peptococci and bacteroides either alone or as a mixed infection. The miscellaneous group comprised of Streptococci, Staphylococcus epidermidis, Diptheroids, Micrococci and Bacilli.

DISCUSSION

In the present study, monomicrobial infections in cases of osteomyelitis were seen in two third of patients while in one third cases the aetiology was polymicrobial. Other studies, from Pakistan as well as abroad ^17,22,23, also report the predominance of monomicrobial aetiology (Table-2). Recent studies^20,24,25 all report an increasing incidence of polymicrobial infection than the series reported in the past^26,27 in which mainly monomicrobial infection was common.

Table-2: Comparison showing percentage of monomicrobial/polymicrobial osteomyelitis

As shown in Table-3, Staphylococcus aureus was the predominant isolate (29.56%). Most studies as  by  Alonge et al²⁰, Lobati  et al¹⁰, Karwowska  et  al¹⁹, Carek et  al²⁸, Marsh  et al²⁵ and  Karamat et al¹⁷  also report  Staphylococcus aureus  as a single organism to be the commonly isolated pathogen from bone infection.

Table-3: Distribution of isolates in various age groups of osteomyelitis patients

Although Staphylococcus aureus remains the most frequent pathogen isolated in bone, the distribution varies from two third Staphylococcus aureus to one third Enteriobacteriaceae or one third each of Staphylococcus aureus, Enteriobacteriaceae and Pseudomonas aeruginosa. This increase in Pseudomonas aeruginosa as a significant bone pathogen is related to the increasing nosocomial nature of osteomyelitis²⁹.

Mousa²³ reported a slight predominance in the isolation rate of Enteriobacteriaceae. Even in our study there was a difference of only 3.24% between Staphylococcus aureus and Enterobacteriaceae group. Enterobacteriaceae are increasingly common nosocomial pathogens²⁹. The third major group in our study was Pseudomonas aeruginosa. Pseudomonas aeruginosa remains a severe complication of hospitalization³⁰. The  total significant  number of cases noted  to be  infected  by the  Entrobacteriaceae  in the present study  could  be due  to blind  therapy  for  presumptive Staphylococcal  aetiology, thus  eliminating some  such cases. Moreover the post-traumatic (69) and post-surgical (48) cases during their hospital stay (114 indoor cases) acquired Klebsiella and Pseudomonas as additional pathogens in the bone. Mixed infections included upto three isolates belonging to   aerobes as Staphylococci, Enterobacteriaceae, Pseudomonas, miscellaneous group or with an anaerobe. Enterbacteriaeiae alone as single organism were isolated in thirty cases and as two organisms in eight cases. Klebsiella was the commonest Entertobacteriaceae to be isolated (21 cases) in single or mixed pattern.

Microorganisms as Staphylococcus epidermidis included in miscellaneous group (5 isolates) have gained importance in periprosthetic infections^31.

This proves the importance of culturing pus from osteomyelitis cases for aerobes, as well as anaerobes for appropriate management and cure of chronic illness.

CONCLUSION

The present study highlights the importance of microbiological examination of bone in cases of osteomyelitis. Microorganisms could not be detected in only 6.6% cases and one third of cases had a polymicrobial aetiology. Any  bacterium, Gram  positive or  negative, aerobe or  anaerobe, either  alone  or as  a mixed  infection, could   be  responsible  for osteomyelitis. 

 The future era with modern high speed travel, warfare, use of implants and prosthetics will add to the load of osteomyelitis.

The clinicians should first obtain a microbiological investigation and then treat their patients to halt the chronic relentless course of this crippling disease.

ACKNOWLEDGEMENT

I am grateful to Dr. N. Rehan, Director Research, PMRC Research Centre, Fatima Jinnah Medical College, Lahore and Liaqat Ali Butt for their support and cooperation.

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Address for Correspondence:

Dr. Faria Malik, 1/C-III, Hussain Chowk, Gulberg III, Lahore. Tele: +92 42 5762152.

Email: fariamalik188@hotmail.com