relationship between air particulate levels and upper respiratory disease in soldiers deployed to Bosnia (1997-1998), The

Military Medicine, Apr 2002 by Hastings, Deborah L

The objective of this study was to determine whether there was a relationship between levels of particulate matter with an aerodynamic diameter of less than 10 (mu)m (PM^sub 10^) and upper respiratory disease (URD) rates in soldiers deployed to Bosnia in 1997 and 1998. PM^sub 10^ levels were divided into quartiles and upper and lower 50th percentiles. When all camps were combined, there was a statistically significant association between the PM^sub 10^ maximum level and URD rates based on KruskalWallis and Mann-Whitney U tests, and the Pearson correlation was statistically significant. Although the relationship was not statistically significant in analyses conducted of the individual camps, the average URD rate increased with each quartile of PM^sub 10^ maximum exposure. There was no statistically significant association between PM^sub 10^, average exposure and URD rates, although the average URD rate increased with each quartile of PM^sub 10^ average exposure. Although these results are not conclusive, there appears to be a relationship between PM^sub 10^ levels and URD rates in soldiers deployed to Bosnia in 1997 and 1998.

Background Air quality has long been associated with respiratory disease; incidents in the 1930s, 1940s, and 1950s, the most famous of which was the "London fog" of 1952, clearly demonstrated that high levels of air pollutants were associated with increases in mortality and morbidity.1 During the last several years, numerous studies in the United States and Europe have shown a remarkably consistent association between air particulate matter and increased mortality. 2-15 The association between air particulates and morbidity has also been examined; significant associations with a variety of health outcomes (hospital admissions, lung function, symptom measures, etc.) have been found.2,12,14,16-18

Both Dockery and Pope19 and Schwartz20 conducted reviews and meta-analyses of the studies on air particulate matter in 1994. Dockery and Pope reported that a series of time-series analyses have shown an approximately 1.0% increase in total deaths per day associated with each 10 (mu)g/m3 increase in the concentration of particulate matter equal to or less than 10 km in aerodynamic diameter (PM^sub 10^). The effect was greater with cardiovascular disease (1.4% per 10 (mu)g/m^sup 3^ PM^sub 10^) and respiratory disease (3.4% per 10 (mu)g/m^sup 3^ PM^sub 10^).19 They also noted that the consistency of these estimates across communities suggests that these results are not attributable to confounding by an unknown or uncontrolled factor and that the mass concentration of the particle mix common to many urban areas, rather than specific chemical species within the mix, may be responsible for the observed associations. In their review of morbidity, Dockery and Pope found that respiratory hospital admissions and emergency department visits increased by approximately 0.8% and 1.0% per 10 (mu)g/m^sup 3^ PM^sub 10^, respectively.19 The increase in emergency department visits and hospital admissions for asthmatics was higher still at 3.4% and 1.9% increase per 10 (mu)g/m^sup 3^ PM^sub 10^.19 Lung function tests showed a modest decrease of approximately 0.15% for forced expiratory volume at 1 second (FEV1) or FEV^sub 0.75^, and a 0.08% decrease for peak flow, per PM^sub 10^ increase of 10 (mu)g/m^sup 3^. Schwartz, examining many of the same studies, concurred. His unweighted meta-analysis yielded a relative risk for mortality of 1.06 (95% confidence interval of 1.05-1.07).20

There is little disagreement that particulate air pollution has adverse health effects. The questions that remain concern the degree of this effect, the particulate level at which the effect occurs, and the populations most affected. What is emerging from the literature is that health effects and dose-response relationships are being observed at relatively low concentrations, much lower than what was once considered safe.2,19.21,22 According to the World Health Organization, "Recent studies suggest that short-term variations in particulate matter exposure are associated with health effects even at very low levels of exposure. The current databases do not allow the derivation of threshold below which no effects exist. Epidemiological studies are unable to define such a threshold, if it exists, precisely."21

Although some longitudinal studies tested the lung function of healthy adults and found acute effects, and hospital usage studies reflect acute effects, many of the measures of morbidity, such as emergency department visits, hospital admissions, and asthma medication use, tended to focus on sensitive subpopulations (children, the elderly, chronic obstructive pulmonary disease patients, asthmatics). One notable exception is a study by Chestnut et al.16 that used National Health and Nutritional Examination Survey I information and compared pulmonary function with ambient air pollution levels, as measured by total suspended particulates. This study excluded individuals with serious respiratory disease and used only individuals who had never smoked. The authors were able to control for individual variation by examining differences in an individual's forced volume capacity (FVC) and FEVI from their predicted FVC and FEV^sub 1^ based on their age, height, weight, and other biological measures. This study showed an effect on both FVC and FEV^sub 1^ at between 60 and 80 (mu)g/m^sup 3^ of total suspended particulate.16 That an effect would be seen in relatively healthy, nonsmoking individuals is of particular importance to the military population. The military has a unique concern for the effect of air pollutants: soldiers are deployed to locations where they may experience higher pollutant levels than they are accustomed to. Any subsequent increase in deleterious health effects can affect a unit's combat readiness. Although military service members are generally healthier than the overall U.S. population, deployment conditions may make them prone to the effects of environmental contamination. This hypothesis has not been tested.