Outbreak of Chlamydia pneumoniae Infections and X-ray-Confirmed Pneumonia in Army Trainees at Fort Leonard Wood, Missouri, 2014.

Introduction: Chlamydia pneumoniae (Cp) is a bacterium that causes pneumonia and other respiratory diseases. Fever may be present early but absent by time of presentation to clinic. Increases in X-ray-confirmed pneumonia (XCP) and laboratory-confirmed Cp infections were observed in new soldiers in training at Fort Leonard Wood (FLW), Missouri, early in 2014. These findings prompted a site assistance visit from the U.S. Army Public Health Command, Aberdeen Proving Ground, Maryland, with a review of available data and information to describe the outbreak, and inspections of barracks and training facilities and review of training practices to identify opportunities for interventions to reduce the risk of respiratory disease agent transmission.

Materials and Methods: The study population was trainee soldiers at FLW in 2013-2014. Data from two acute respiratory disease surveillance systems were studied. A local surveillance system operated by the FLW General Leonard Wood Army Community Hospital Preventive Medicine Department tracked weekly chest X-rays taken and the numbers positive for pneumonia. A Naval Health Research Center, San Diego, California, laboratory-based Febrile Respiratory Illness Surveillance Program collected clinical data and nasal, or nasal and pharyngeal swabs, for nucleic acid amplification testing from up to 15 trainees/week with fever and either cough or sore throat. Up to 4 of the 15 specimens could be from afebrile patients with XCP. Specimens were tested for a variety of agents.

Results: Monthly rates of XCP rose quickly in 2014 and peaked at 0.9/100 trainees in May. The percentage of the San Diego surveillance system specimens that were positive for Cp also increased quickly in 2014, peaking at 54% in May. During the first half of 2014, the San Diego program studied specimens from 141 ill trainees; 37% (52/141) were positive for Cp, making it the most common organism identified, followed by rhinoviruses (8%), influenza viruses (4%), Mycoplasma pneumoniae (2%), and adenoviruses (1%). The remaining specimens (48%) were negative for all respiratory pathogens. Only 12% (6/52) of Cp positive patients were febrile. Facilities inspections and review of training practices failed to identify variables that might be contributing to an increased risk of respiratory agent transmission.

Conclusion: The XCP rate and the percentage of specimens positive for Cp increased in early 2014, peaking in May. Only 12% of trainees with laboratory-confirmed Cp were febrile. Historically, acute respiratory disease surveillance at military training centers focused on febrile diseases, particularly those caused by adenoviruses. With introduction of an adenovirus vaccine in late 2011, respiratory disease rates dropped with only sporadic occurrences of adenovirus-associated disease. In 2012, the San Diego surveillance program began providing data on multiple respiratory disease agents, in addition to adenoviruses and influenza viruses. Since then, Cp, rhinoviruses and Mycoplasma pneumoniae have frequently been detected in trainees with acute respiratory disease. Respiratory surveillance programs supporting Army training centers should be re-evaluated in this post-adenovirus vaccine era, to include assessment of the fever criterion for selecting patients for study, the value of chest X-ray surveillance and the value of rapidly providing laboratory results to inform provider decisions regarding antibiotic use.