To the Editors:

I read the recent article by Gouveia et al1 in which the risk factors for acute complications and late orthopedic sequelae were analyzed separately in 240 children with skeletal system infections. Using a multivariable logistic predictive model, age older than 4 years, a culture-proven Staphylococcus aureus etiology, fever at admission, C-reactive protein level >100 mg/L and osteomyelitis were associated with increased risk for an acute complicated course.1 Age ≥4 years, a C-reactive protein level ≥110 mg/L, disseminated disease and formation of bone abscesses predicted long-term disability.1 The flip side of the study results implies that afebrile patients younger than 4 years of age, without a staphylococcal infection and presenting with low concentrations of acute phase reactants have a better acute and long-term prognosis.

Overall, S. aureus was the most recovered pathogen and was isolated in 32 (13.3%) patients, followed by Kingella kingae, which was detected in 29 patients (12.1%), whereas no pathogen was identified in 150 children (62.5%) (!). Because of the retrospective nature of the study spanning 11 years, in most cases, the bacteriologic diagnosis of the disease was attempted by traditional culture methods, whereas the use of molecular tests was limited to the later stages of the study.

Whereas conventional cultures recover S. aureus without difficulty, K. kingae is notoriously fastidious.2 Its detection requires the inoculation of synovial fluid aspirates and bone exudates into blood culture vials2 and, especially, the use of sensitive species-specific nucleic acid amplification tests.3

In recent years, the consistent use of nucleic acid amplification tests has resulted in the recognition of K. kingae as the prime agent of joint and bone infections in children 6–48 months of age, causing up to 87.7% of the episodes of septic arthritis in this age group.3 The clinical and laboratory presentation of children with K. kingae disease is subtle and atypical, requiring a high index of suspicion. In a report by Cochard et al4 that included 247 pediatric patients with K. kingae-proven osteoarticular infections, the mean ± standard deviation age was 18.5 ± 10 months and only 4 (1.6%) children were older than 48 months of age, and the mean ± standard deviation C-reactive protein concentration was 26.6 ± 27.8 mg/L. Moreover, with rare exceptions, pediatric K. kingae skeletal system infections usually follow an uncomplicated course, promptly respond to adequate antimicrobial therapy and do not leave long-term functional disabilities.3,4 These demographic, clinical and biologic features are remarkably similar to those found by Gouveia et al1 among children in whom the etiology of the infection remained undetermined.

In summary, the results of the Gouveia et al study suggest that many of the mild and uncomplicated infections reported in the article were caused by undetected K. kingae infections, emphasizing the need to use K. kingae-specific molecular methods in the diagnosis of skeletal system infections in young children.

REFERENCES 1. Gouveia C, Subtil A, Aguiar P, et al. Osteoarticular infections: younger children with septic arthritis and low inflammatory patterns have a better prognosis in a European cohort. Pediatr Infect Dis J. 2023;42:969–974. 2. Yagupsky P, Dagan R, Howard CW, et al. High prevalence of Kingella kingae in joint fluid from children with septic arthritis revealed by the BACTEC blood culture system. J Clin Microbiol. 1992;30:1278–1281. 3. Juchler C, Spyropoulou V, Wagner N, et al. The contemporary bacteriologic epidemiology of osteoarticular infections in children in Switzerland. J Pediatr. 2018;194:190–196.e1. 4. Cochard B, De Marco G, Bazin L, et al. Biological predictors of osteoarticular infection due to K. kingae–a retrospective cohort study of 247 cases. Microorganisms. 2023;11:2130.