Pneumonia outbreak associated with group A Streptococcus species at a military training facility

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 130 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.