Background: Although group A streptococci (GAS) infections are a major cause of morbidity and mortality, outbreaks of associated pneumonia are rare. We report an outbreak of GAS pneumonia that occurred at a US military training camp.
Methods: Standard epidemiologic and laboratory procedures were used to characterize the outbreak and causative organism(s). A case-control study and determination of the prevalence of GAS infection among camp personnel were also performed.
Results: A total of 162 of 4500 Marine Corps personnel were hospitalized for respiratory symptoms during the period of 1 November and 20 December 2002, and 127 (78%) had radiographically confirmed pneumonia. The attack rate was 1.6 cases per 100 person-months. Thirty-four (27%) of 127 patients with pneumonitis had definite or probable GAS pneumonia; an additional 22 (17.3%) were coinfected with GAS and another pathogen. Pathogens, in addition to GAS, included Chlamydia pneumoniae (27 patients), Mycoplasma pneumoniae (19), adenovirus (5), and Streptococcus pneumoniae (2). A survey revealed that the pharyngeal carriage rate of GAS among camp personnel was 16%. Molecular characterization of the GAS isolates found emm type 3, multilocus sequence type 15. The epidemic ended after administration of additional prophylaxis with a single dose of intramuscular benzathine penicillin (1.2 million U) or azithromycin (1 g orally). Because the number of days from the last penicillin injection was correlated with a positive throat culture result and the occurrence of pneumonia, the dosing interval of benzathine penicillin was shortened from every 28-35 days to every 21 days.
Conclusions: This is the largest outbreak of GAS pneumonia reported in >30 years. This outbreak emphasizes the potential for GAS to cause epidemics of severe infection and demonstrates the need for surveillance and consideration of appropriate antibiotic prophylaxis among particularly high-risk populations.