Original Contribution

Etiology of Septic arthritis in children: an update for the new millennium

Timothy P. Young MD?, Lee Maas MD, Andrea W. Thorp MD, Lance Brown MD

Division of Pediatric Emergency Medicine, Department of Emergency Medicine, Loma Linda University Children’s Hospital, Loma Linda, CA 92354, USA

Received 10 December 2009; revised 2 April 2010; accepted 3 April 2010

Abstract

Objective: We sought to describe the causative organisms and joints involved in cases of pediatric septic arthritis in the post-Haemophilus influenzae type B and post-pneumococcal vaccine age and in the age of increasing infection with community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA).

Methods: This was a retrospective chart review of all children younger than 13 years presenting to our tertiary care pediatric emergency department between January 1, 2003, and December 31, 2007, with the diagnosis of septic arthritis. We reviewed the results of synovial fluid Gram stain and synovial fluid and blood culture. We defined septic arthritis as any of these 3 tests being positive for a known pathogen. We report patient characteristics, joint(s) involved, and organisms identified in these cases.

Results: We describe 13 cases of septic arthritis. Fifteen joints were involved. The most common joint involved was the hip (6/15) followed by the elbow (3/15), knee (2/15), and ankle (2/15). The most common organism involved was methicillin-sensitive S aureus (6/13), followed by CA-MRSA (2/13) and Streptococcus pneumoniae (2/13).

Conclusion: Our results support continued concern for involvement of the hip and knee in cases of pediatric septic arthritis and consideration of other joints such as the elbow. Our data also suggest that empiric antibiotic coverage for CA-MRSA is indicated in cases of pediatric septic arthritis, as well as continued coverage for methicillin-sensitive S aureus and S pneumoniae.

(C) 2011

Introduction

Septic arthritis in the pediatric population presents a diagnostic and therapeutic challenge to emergency physi- cians. Historically, the joints of greatest concern have been the knee and hip. The most common organisms implicated have been methicillin-sensitive Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus

* Corresponding author. Department of Emergency Medicine, Loma Linda University Medical Center, Loma Linda, CA 92354, USA.

E-mail address: [email protected] (T.P. Young).

influenzae [1]. Recent years have seen the remarkable success of the H influenzae type B vaccine, with a resultant decrease in the incidence of H influenzae type B septic arthritis [2,3]. More recently, the heptavalent S pneumoniae vaccine has come into widespread use in the United States, and soft tissue infections from community- associated methicillin-resistant S aureus (CA-MRSA) have become commonplace [4,5]. Our recent clinical experience suggested a change in the epidemiology of septic arthritis. The presence of CA-MRSA joint infections and infections involving joints other than the hip and knee seemed to be on the rise.

0735-6757/$ – see front matter (C) 2011 doi:10.1016/j.ajem.2010.04.008

To our knowledge, no study has attempted to describe these recent changes in the emergency department presentation of pediatric septic arthritis. The objective of our study was to describe septic arthritis cases involving prepubescent children seen in our pediatric emergency department over a 5-year period from 2003 to 2007. Our primary interests were identifying the joints involved and the incidence of CA-MRSA and S pneumoniae infections.

Materials and methods

We performed a retrospective medical record review of all children younger than 13 years presenting to the pediatric emergency department at our university-based, tertiary care institution between January 1, 2003, and December 31, 2007, with the diagnosis of septic arthritis. Subjects were identified by the ICD-9 Diagnostic codes for septic arthritis (711.00-711.99).

We used a standardized data collection form. Data were collected by a trained data abstractor who was not blinded to the study objective. The data extracted from the medical records were the patient’s age, sex, joint(s) involved, presence of comorbidities, previous surgeries, previous diagnosis of bone or joint infection, antibiotics given, and results of Synovial fluid analysis, synovial fluid culture, and blood culture.

A positive evaluation for septic arthritis was defined by the presence of positive synovial fluid or blood culture for a known pathogen or identification of a likely pathogen on Gram stain of synovial fluid. We considered “known pathogens” to be organisms other than coagulase-negative staphylococcus and diphtheroids. Gram stains positive for gram-positive cocci in clusters were considered positive because of the inability to distinguish S aureus and Staphylococcus epidermidis on Gram stain, except when culture results confirmed coagulase-negative staphylococci. We considered gram- positive bacilli on Gram stain to be contaminants.

Exclusion criteria were previously diagnosed bone or joint infection involving the affected joint, a history of previous surgery on the affected joint, incomplete/missing medical records, and chronic illness. Chronic illness was defined as the presence of a ventriculoperitoneal shunt, the presence of an indwelling central venous catheter, or tracheostomy/ventilator dependence. Subjects were also excluded when there was no joint fluid sampling available. Descriptive statistics were used and calculated using Excel 2008 for Macintosh Version 12.0 (Microsoft Corporation, Redmond, WA). Where 95% confidence intervals are reported, the adjusted Wald method was used and was calculated using STATA 9.1 (Statacorp LP, College Station, TX). This study was approved by our institutional review board.

Results

We identified 53 unique patient encounters with an ICD-9 code for septic arthritis during the 5-year period. All medical records were complete. A total of 13 encounters met our exclusion criteria. This resulted in a group of 40 unique subjects who were evaluated for septic arthritis. Twenty- seven subjects had a negative evaluation for septic arthritis. Therefore, our main study group consisted of the remaining 13 subjects (Fig. 1). Eight (62%) were male. The median age was 3 years (interquartile range, 6 months to 8 years; range, 3 months to 12 years) (Fig. 2). From these 13 subjects, 15 joints had septic arthritis. An 11-year-old boy had simulta- neous septic arthritis in both hips and the right elbow.

The most common joint involved was the hip, followed by the elbow, knee, and ankle (Fig. 3). In all cases where a likely pathogen was identified by gram stain, a pathogen was also isolated by blood or synovial fluid culture. The most common pathogenic organism isolated was methicillin- sensitive S aureus, followed by CA-MRSA and S pneumo- niae (Table 1). H influenzae was isolated in 1 subject. There was no typing available for this H influenzae isolate.

Fig. 1 Subject flow diagram. ?Tracheostomy/ventilator depen- dent, indwelling Central venous line, or presence of ventriculoper- itoneal shunt. ⁺Two subjects with septic bursitis, 1 with acute cerebellar ataxia and 1 with psoas abscess. ^?Fifteen joints in 13 subjects (1 subject with 3 joints involved).

Fig. 2 age distribution of children with septic arthritis (n = 13).

Table 1 Pathogenic organisms isolated

Of note, both isolates of CA-MRSA were sensitive to vancomycin and trimethoprim-sulfamethoxazole, with 1 of the isolates being resistant to clindamycin and tetracycline.

Discussion

Our results support continued concern regarding septic arthritis of the hip and knee and increased concern with respect to CA-MRSA in pediatric septic arthritis. However, we did find a relatively high prevalence of septic arthritis of the elbow, which has not been previously described as one of the more common joints associated with septic arthritis. Likewise, septic arthritis of the ankle was fairly common in our sample.

We found a relatively high incidence of septic arthritis caused by CA-MRSA, further supporting recent findings in the orthopedic literature [6,7]. Similar findings have also

Fig. 3 Joints involved (n = 15). ?One subject had multiple joints involved, for a total of 15 joints in 13 patients.

recently been reported regarding septic arthritis in adult patients in the emergency department setting [8], and invasive bacterial infections as a whole attributed to CA- MRSA appear to be on the rise [9].

Our findings also support continued concern for S pneumoniae as a causative organism in pediatric septic arthritis. The heptavalent vaccine has been shown to provide impressive but incomplete protection against the organism, likely due to nonvaccine serotypes [10].

There is no broadly accepted reference standard for the diagnosis of septic arthritis. We based our definition of septic arthritis on a widely cited meta-analysis that included studies defining septic arthritis by positive synovial fluid Gram stain, positive blood culture, positive synovial fluid culture, macroscopic pus obtained from the joint, or response to antibiotics [11]. We chose to narrow our definition of septic arthritis to include only subjects with a positive synovial fluid Gram stain or positive synovial fluid or blood culture due to the subjective nature of the other 2 criteria.

We included subjects younger than 13 years. Our intention was to exclude sexually active subjects who would be at higher risk for infection with Neisseria gonorrhoeae. We did not have any cases of N gonorrhoeae in this study.

• 1. Limitations

We report on a small number of children. Given this, it is unclear if the high percentage of subjects with septic arthritis of the elbow represents a true shift in the epidemiology of joint involvement. Because our laboratory did not routinely test for H influenzae typing during the time of this study, we were unable to determine if the H influenzae isolate was type

b. Similarly, we were unable to determine if the cases of S pneumoniae septic arthritis were caused by subtypes covered by the heptavalent vaccine.

Conclusion

Our data suggest that empiric antibiotic coverage for CA- MRSA is indicated for cases of suspected pediatric septic

arthritis. Our results support continued concern for S pneumoniae as a cause of pediatric septic arthritis despite the introduction of the heptavalent vaccine. Our data also suggest that the hip and knee continue to be associated with septic arthritis, but that other joints such as the elbow and ankle may also be affected.

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