Epidemiological features of invasive Kingella kingae infections and respiratory carriage of the organism

The age, sex, and seasonal distributions of invasive Kingella kingae infections in southern Israel were examined and compared to the epidemiology of respiratory carriage of the organism. Medical records of all patients diagnosed between 1988 and 2002 were reviewed, and 2,044 oropharyngeal specimens were cultured on selective media during two periods (February to May and October to December) in 2001. Invasive infections significantly affected children (73 of 74 patients [98.6%] were younger than 4 years), 50 patients (67.8%) were males (P = 0.045), and 55 episodes (74.3%) occurred between July and December (P = 0.004). Carriage was higher in the 0- to 3-year-old group and decreased with increasing age (P for trend = 0.0008). Carriage rates were similar in both sexes and did not significantly differ between the February-to-May and October-to-December periods. The highest rate of carriage of K. kingae coincided with the age (less than 4 years) at which invasive infections were especially frequent. The peculiar sex and seasonal distributions of invasive disease, however, cannot be readily explained by the epidemiology of respiratory carriage. Viral infections and other yet-to-be-defined cofactors may play a role in the causation of invasive K. kingae infections.