Septic Arthritis in a 14-Month-Old Child

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


April 12, 2010

In This Article

Clinical History

A 14-month-old girl presented to the emergency department with history of low-grade fevers (38.5oC). The child was the product of a full-term delivery and was meeting all milestones. However, the mother reported that the child had started refusing to walk several days before presentation and had been "abnormally fussy" secondary to teething and stomatitis. The right knee was slightly swollen and painful upon movement during physical examination. Fluid was aspirated from the right knee, which showed 30,000 leukocytes with a neutrophil predominance of 80%. C-reactive protein was elevated at 3.0 mg/dL (normal, 0.0-0.9 mg/dL). No organisms were seen on direct Gram stain. The child was started on empiric broad-spectrum antibiotic therapy with ceftriaxone and vancomycin.

Direct culture of the synovial fluid on routine media demonstrated no growth at 4 days. Additional knee fluid was sent for broth enriched culture in aerobic and anaerobic blood culture bottles. Both bottles demonstrated growth of a gram-negative rod after 37 hours' incubation. Subculture of the broth demonstrated very small colonies at 24 hours incubation on blood (Figure 1a) and chocolate agar, but no growth on MacConkey agar. Colonies were faintly beta-hemolytic (Figure 1c). The Gram stain from the solid medium is shown in Figure 2. The organism was oxidase-positive and catalase-negative.

Figure 1. Colonial growth morphology: (a) blood agar plate at 24 hours demonstrating small, clear colonies; (b) blood agar plate at 48 hours demonstrating more luxurious growth of the organism; (c) blood agar plate demonstrating soft beta hemolysis.
Figure 2. Gram stain of the joint fluid from the broth enrichment culture. The Gram-stained preparation demonstrates gram-negative rods in pairs and short chains. The rods measure 0.6-1 uM x 1-3 uM and demonstrate tapered ends. Kingella kingae may under-decolorize when staining and thus be mistaken for gram-positive rods.

What is the diagnosis and what should be included in the differential of septic arthritis in a child under 2 years of age?