Kingella kingae most often causes acute septic arthritis

An observational study conducted in Portugal found that Kingella kingae has displaced Staphylococcus aureus as the most common causative organism of acute septic arthritis (SA). The investigation also revealed that older children with comorbidities are at increased risk of SA sequelae.

Investigators analyzed data of children admitted to a hospital with SA from 2003 through 2018. Diagnosis of acute SA and osteomyelitis was based on classical clinical findings plus suggestive imaging. Investigators identified 247 children with the diagnosis, almost 60% of whom were male, with a median age of 2 years. During the last 5 years of the study period, annual incidence increased 1.7-fold, and diagnosis occurred at a lower median age. Respiratory tract infection (in 23.5% of patients) most often preceded diagnosis, followed by trauma, cutaneous wounds, and chickenpox. The most common clinical presentations were pain and range of motion limitations, followed by fever, local inflammatory signs, and toxic appearance. Hip joints were affected most often (38.9% of patients), followed by knee, ankle, elbow, and shoulder joints.

Before 2014, 37% of SA cases were caused by a pathogen. The most common was S aureus (in 65.3% of those with microbiologic etiology), followed by Streptococcus pyogenes (12.2%), and Streptococcus pneumoniae (10.2%). K kingae, Haemophilus influenzae b, Neisseria meningitidis, Escherichia coli, Streptococcus mitis, and Salmonella spp each accounted for 2% of SA cases. After 2014, a causative pathogen was found in 49% of cases, led by K kingae (found in 51.9% of those with microbiologic etiology), followed by S aureus (19.2%), S pyogenes (9.6%), S pneumoniae (5.8%), N meningitidis (5.8%), H influenzae b (1.9%), Enterobacter spp (3.8%), and Brucella (1.9%). In the last 5 years of the study period, children tended to be treated intravenously for fewer days than earlier (10.7 vs 13.2) but had more complications (20.6% vs 11.4%). Risk factors for complications were C-reactive protein (CRP) ≥ 80 mg/ L and S aureus infection, and for sequelae at 6 months being 4 years or older, having underlying chronic disease, and a CRP ≥ 80 mg /L.

Thoughts from Dr. Farber

I don't believe I heard of this bacterium at all during medical school, only subsequently with osteomyelitis (but at first just in patients with sickle cell anemia disease). Not surprisingly, we now recognize it as a major cause of septic arthritis. Remember to cover for it (note that vancomycin and clindamycin are not effective) while waiting for culture results.

Reference

1. Gouveia C, Duarte M, Norte S, et al. Kingella kingae displaced S. aureus as the most common cause of acute septic arthritis in children of all ages. Pediatr Infect Dis J. 2021;40(7):623-627. doi:10.1097/INF.0000000000003105