We describe an outbreak of radiologically-confirmed pneumonia that was first recognized in a military training company after two fatal cases of pneumococcal meningitis caused by serotype 7F occurred in the same company. Overall, 15% of trainees in the 554th Battalion were colonized with pneumococcus, and serotypes 7F and 3 were predominant. Colonization rates of 14-44% have been documented among military personnel in the setting of other pneumococcal outbreaks[4, 7, 8]. Because pneumococcus is the most common bacterial cause of pneumonia and meningitis in the United States, C. pneumoniae detection among 44% of trainees tested was unexpected and suggests a possible outbreak of C. pneumoniae infection in the same battalion.
Most adults with pneumonia, whether civilian or military, do not undergo etiologic testing for pneumonia. Our investigation began after 21 trainees in the 554th Battalion had already been diagnosed with pneumonia and treated with antibiotics. Thus, the etiology of their pneumonia remains unclear. Pneumococcus has been documented as the primary etiologic agent in several outbreaks of pneumonia among military trainees described in the literature[1, 4–6, 8, 15]. During this outbreak of pneumonia at FLW training camp, the isolation of pneumococcus serotype 7F from the CSF of the two trainees with fatal meningitis and the predominance of serotypes 7F and 3 among trainees from their battalion may indicate that increased pneumococcal transmission was occurring at the time of the outbreak and provides some indirect support for pneumococcus as a possible etiologic agent or cofactor in the outbreak of pneumonia. However, blood cultures were obtained at the time of pneumonia diagnosis from only three trainees with pneumonia, all of whom had cultures with no growth, and pneumococcal urinary antigen testing was not performed for any of the trainees with pneumonia.
C. pneumoniae may have also played a role in this outbreak of pneumonia, either as a primary etiologic agent or as a cofactor, as suggested by the increased prevalence of C. pneumoniae identification among trainees in the battalion compared to training staff and incoming trainees. C. pneumoniae is recognized as a common cause of community acquired pneumonia in young adults, and two outbreaks of pneumonia associated with C. pneumoniae have been documented among military recruits in Europe[3, 16]. One study conducted in a Finnish civilian population also suggested that C. pneumoniae infection can predispose individuals to subsequent infection with S. pneumoniae.
Every year, approximately 68,500 individuals participate in training at FLW training camp, and typically 12,000-15,000 trainees are at the training camp at any given time. The constant turn-over of trainees at military training facilities poses a challenge for timely rate-based surveillance at the company level because the number of trainees at risk changes every one to two weeks. In this investigation, the outbreak of pneumonia among Alpha and Hotel Company trainees was identified by the GLWACH medical command, in part because of the two fatal cases of pneumococcal meningitis, as well as through GLWACH's surveillance for radiologically-confirmed pneumonia. To facilitate outbreak detection and response, including antibiotic prophylaxis and vaccination when indicated, on-going, timely analysis of surveillance data at the company level at military training installations should be considered.
PPV23 and antibiotic prophylaxis, primarily with benzathine penicillin G, were used in an attempt to halt this outbreak because the serotype that caused the two cases of meningitis is included in PPV23 and was susceptible to penicillin. In the absence of a control group with similarly high attack rates of pneumonia, we were unable to determine the effectiveness of PPV23 or chemoprophylaxis in preventing further cases of pneumonia or meningitis. PPV23 and antibiotic prophylaxis have previously been used in other clusters of severe pneumococcal infection  including in military settings[4, 6]. Since most PPV23 recipients require two weeks to develop immunity after vaccination, antibiotic prophylaxis has been used as an adjunct in outbreak settings to provide additional protection until immunity has developed. Antibiotic prophylaxis against pneumococcus can also decrease nasopharyngeal colonization with pneumococcus and decrease pneumococcal transmission.
Pneumococcal vaccination is a proven method of prevention of pneumococcal disease. Vaccination with PPV23 was provisionally recommended for smokers and persons with asthma by the Advisory Committee on Immunization Practices (ACIP) at the time of this investigation and is now officially recommended for these groups by the ACIP. The Military Vaccine Agency does not recommend vaccination with PPV23 for all military trainees but does offer the vaccine to those considered at high risk of pneumococcal infection. The potential licensure of pneumococcal conjugate vaccines for adults in the United States may benefit military trainees because such vaccines prevent colonization with and transmission of vaccine-type pneumococci. The advent of pneumococcal common protein vaccines, which would provide protection against all serotypes of S. pneumoniae, may offer another opportunity for prevention of pneumococcal disease among military trainees in the future.
Our investigation was subject to at least two limitations. First, since our investigation began after the majority of pneumonia cases had occurred in the 554th Battalion, we relied, in part, on diagnostic tests performed by the treating clinician at the time of pneumonia diagnosis to try to identify the etiology of the outbreak of pneumonia, and these diagnostic tests were not performed in a systematic manner. Second, since this investigation was undertaken as part of a public health response, we could not survey and obtain respiratory specimens from an unaffected training company with a lower pneumonia attack rate for comparison to trainees in the Alpha and Hotel companies. Inclusion of such a comparison group would have provided data on pneumococcal carriage and C. pneumoniae detection rates among trainees with a lower rate of pneumonia who were living and training under similar condition as Alpha and Hotel company trainees.