COMMENTARY

Septic Arthritis in a 14-Month-Old Child

Jeanette M. Ramos, MD; Julie A. Ribes, MD, PhD

Disclosures

April 12, 2010

In This Article

Diagnosis

This is a case of joint infection caused by K kingae. K kingae is a fastidious gram-negative rod within the family Neisseriaceae. Its growth characteristics include slow growth on blood agar with the production of soft beta hemolysis. It fails to grow on MacConkey agar. The organism is oxidase-positive and urease-, indole-, and catalase-negative. It is capable of producing acids from glucose and maltose but no other sugars.[4] In this case, a definitive identification was made using the BD Phoenix Automated Microbiology System (BD Diagnostics; Sparks, Maryland).

Another key growth characteristic of this organism is its reluctance to grow in direct culture from septic joint fluids. Dr. Pablo Yagupsky demonstrated that inoculating joint fluid into aerobic blood culture bottles led to an increased incidence of K kingae in the joint fluids of young children.[1] In this study of 216 children with joint infections, synovial cultures were performed by routine culture and/or culture using a broth-enrichment blood culture system. The majority of children demonstrated infection with Staphylococcus aureus (36.5% of infections). The second most common isolate in this series was K kingae, representing 22.2% of isolates. Brucella melitensis, Streptococcus pyogenes, Streptococcus pneumoniae, group C streptococcus, Haemophilus influenzae, and rarely Neisseria meningitidis or Escherichia coli were also seen as joint pathogens. This study demonstrated that the Bactec broth enrichment blood culture system (Organon Teknika; Durham, North Carolina) was comparable to direct culture of the synovial fluid for all pathogens except K kingae. The majority of K kingae infections were detected by the broth-enrichment blood culture system only. Cultures with K kingae became positive in a median of 3.5 days, with the rare culture requiring extended incubation to produce clinical isolates. Following the study by Yagupsky and colleagues, many laboratorians have demonstrated increased detection of this organism when using blood culture broth-enrichment medium bottles from other manufacturers.[5,6,7]

It is hypothesized that inhibitors in the highly inflamed synovial fluid impede the direct growth of organisms on solid medium. These inhibitors are significantly diluted in blood culture bottles, potentially allowing for the growth of this fastidious organism.[8] Because of these findings, the Centers for Disease Control and Prevention (CDC) has recommended the routine use of an aerobic blood culture bottle for a broth enrichment culture to detect K kingae from synovial fluids.[9] More recently, PCR assays performed on synovial fluids cultured in aerobic blood culture bottles have been used to demonstrate K kingae DNA in the joint fluid of about half of the culture-negative patients in one series, suggesting that the prevalence of this organism in causing septic arthritis is dramatically underestimated.[3]

Disease Processes Associated With Kingella kingae

K kingae is most commonly associated with monoarticular septic arthritis syndrome in previously healthy children under 2 years of age. The joints most commonly infected are the large weight-bearing joints (hip, knee, and ankle), the knees being the most frequently involved. Of the non-weight-bearing joints, the wrist is most commonly involved.[4,10] Osteomyelitis may also be seen, most frequently involving the femur, calcaneus, and talus bones.[4] Infections of the vertebral disc, cellulitis, infections of bursae and tendons, and subcutaneous abscess formation have also been described in young children.[4]

K kingae is also associated with bacteremia and infective endocarditis.[4] It is one of the HACEK organisms (Haemophilus species, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella species). The HACEK organisms are mouth flora that may hematogenously spread when there is a disruption of oral mucosal integrity, such as in cases of dental/periodontal disease or teething. These organisms were grouped together because of their fastidious nature and their association with "culture-negative" endocarditis. In the past, culture for these organisms required long incubation periods (2 or more weeks) and blind terminal culture onto solid medium. Because of the optimization of broth-enriched blood culture systems, the HACEK organisms are now often isolated during routine culture with a standard 5-day incubation period.[11] If extended incubation is requested by the ordering physician to rule out endocarditis, Clinical and Laboratory Standards Institute (CLSI) guidelines recommend subculture of all bottles onto chocolate and blood agar plates instead of extended incubation of the bottles themselves. Transient bloodstream infections without endocarditis are seen mostly in young children, whereas endocarditis is most commonly seen in school-aged children, adolescents, and adults.[4] Endocarditis with Kingella species generally occurs in the setting of preexisting heart and valvular abnormalities, including rheumatic heart disease, congenital heart defects, abnormal native valves, and prosthetic valves. Rarely it may occur in individuals whose valves were previously normal.[4]

Of note, bacteremia is only rarely detected in children with joint infections.[3,6,10,12] In this current case, blood cultures were sent, but no growth was detected at 5 days. In response to a request from the ordering physician, the cultures were held for 2 weeks. At 9.6 days, both bottles from one of the cultures demonstrated growth of Propionibacterium acnes.

Epidemiology

Similar to the other HACEK organisms, K kingae is part of the normal oral flora. It has been identified as a colonizer of the oropharynx in asymptomatic populations and in individuals who have developed invasive disease.[13,14,15,16,17] Child-to-child transmission, likely through oral secretions, has been suggested by studies looking at family units and daycare centers.[12,14,16,17] The highest level of colonization is seen in children under 3 years of age, the group in which most invasive disease occurs.[15,17] Although no gender difference exists for colonized children, there is a male predominance (67.8%) for invasive disease.[15] Predisposing features for developing active disease include preceding upper respiratory infections, hand-foot-and-mouth disease, stomatitis, aphthous ulcers of the mouth, tonsillar abscess, other oral lesions, otitis media, and diarrhea.[10,12,15,16,18,19] For infections seen in Israel, an apparent seasonality between July and December has been suggested.[19]

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