Acute respiratory illnesses (ARIs) are among the leading causes for hospital visits in U.S. military training populations and historically peak during U.S. Army Basic Combat Training (BCT) following mandatory exposure to the riot control agent o-chlorobenzylidene malononitrile (CS). This observational prospective cohort studied the association between CS exposures and ARI-related health outcomes in 6,723 U.S. Army recruits attending BCT at Fort Jackson, South Carolina from August 1 to September 25, 2012 by capturing and linking the incidence of ARI before and after the mask confidence chamber to CS exposure data. Recruits had a significantly higher risk (risk ratio = 2.44; 95% confidence interval = 1.74, 3.43) of being diagnosed with ARI following exposure to CS compared to the period of training preceding exposure, and incidence of ARI after CS exposure was dependent on the CS exposure concentration (p = 0.03). There was a significant pre-/postexposure ARI difference across all CS concentration levels (p < 0.01), however, no significant differences were detected among these rate ratios (p = 0.72). As CS exposure is positively associated with ARI health outcomes in this population, interventions designed to reduce respiratory exposures could result in decreased hospital burden and lost training time in the U.S. Army BCT population.

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Background Acute respiratory infections (ARIs) are the leading cause of acute morbidity and lost work time in the United States. Few studies have looked at building design and transmission of ARIs. Objectives This study explores the association of ventilation design, room occupancy numbers, and training week with ARI rates in Army Basic Combat Training barracks. Methods This observational study captured the overall incidence of ARI in a cohort of 16,258 individuals attending basic combat training at Fort Jackson, South Carolina. Results ARI risk was higher among trainees living in the 60-person room barracks compared with those living in 8-person rooms, which increased rapidly for the first few weeks of training and then declined to baseline. Conclusions Findings support direct contact as primary ARI transmission mode in this study population based on observed lower ARI risk in smaller room barracks and similar risk in large room barracks despite heating, ventilation, and air conditioning system variability.

Exposing unmasked US Army recruits to elevated levels of o-chlorobenzylidene malononitrile (CS tear gas) during Mask Confidence Training (MCT) increases the risk of Acute Respiratory Illness (ARI) diagnosis in the period following CS exposure when compared to the period before exposure. All Army Activities Message (ALARACT) 051/2013 was implemented in March 2013 to reduce CS exposure concentrations during MCT and associated ARI rates. This observational, prospective cohort studied CS exposures and associated ARI health outcomes after implementation of ALARACT 051/2013 in 5 298 recruits attending US Army Basic Combat Training (BCT). These data indicate a 10-fold reduction (p<0.001) in CS exposure concentrations; recruit exposures ranged from 0.26 -2.78 mg/m 3 ( =1.04 mg/m 3 ) and chamber operator exposures from 0.05 -2.22 mg/m 3 ( =1.05 mg/m 3 ). The overall risk of ARI diagnosis following CS exposure also decreased when compared to period before exposure (RR=1.79, 95%CI=1.29, 2.47) resulting in 26.85% (95%CI=-0.17, 0.54) intervention effectiveness. Post-chamber ARI rates were dependent upon CS exposure concentration (p=0.02), and pre/post-chamber ARI rate ratios were significantly elevated at all concentration categories higher than the Threshold Limit Value Ceiling (TLV-C) (0.39 mg/m 3 ). Results support previous research suggesting risk of ARI diagnosis after CS exposure is positively associated with CS concentration.

There is great interest in preventing the spread of acute respiratory infections (ARI) in military housing and in other facilities with multiple occupants such as hospitals. There has been some research on the mode of transmission of ARIs in these types of occupancies, with several studies focusing on direct and indirect contact. This study, based on several barracks at the largest basic training facility for the Army in the United States, investigates the role of airborne transmission via heating, ventilating and air conditioning (HVAC) systems as compared to a combination of airborne, indirect contact and direct contact transmission in a room. The results indicate that there is a significant increase in the number of cases which might be attributable to airborne transmission via HVAC systems in several situations, both for ARIs that required hospitalization, and those which did not.