Methodological challenges of using U.S. Army administrative data to identify a cohort of basic combat trainees and descriptive analysis of trends in characteristics that are potential risk factors for training-related injury.

OBJECTIVES: Training-related injury is a threat to military health and readiness. Prevalence of potential risk factors for training-related injury can change with U.S. Army recruitment goals and may influence basic combat training (BCT) injury rates. This article describes challenges of using administrative data to identify a trainee cohort and describes demographic and training characteristics across the five BCT locations. METHODS: Data from the Total Army Injury and Health Outcomes Database were used to identify a U.S. Army-wide cohort of first-time trainees from January 1, 2002 to September 30, 2007 and describe its characteristics. RESULTS: The cohort includes 368,102 first-time trainees. The annual number starting BCT increased from 52,187 in 2002 to 68,808 in 2004. The proportion of males increased from 81.57% in 2003 to 83.84% in 2007. Mean (SD) age increased from 20.67 (3.55) years in 2002 to 20.94 (3.65) years in 2007. Mean (SD) body mass index increased from 24.53 (3.56) kg/m(2) in 2002 to 24.94 (3.84) kg/m(2) in 2006. Other characteristics fluctuated by year, including proportions of race/ethnicity, accession waivers, and confirmed graduates. CONCLUSIONS: Fluctuations in trainee characteristics warrant further analysis of potential influence on BCT injury rates. For research uses, careful acquisition of administrative data is needed.

Disability among US Army Veterans vaccinated against anthrax.

CONTEXT: To protect troops against the use of anthrax as a biological weapon, the US Department of Defense began an anthrax vaccination program in 1998. 14 years after the inception of the vaccination program, there is no evidence suggesting vaccination against anthrax carries long-term health risks for Active Duty Soldiers. OBJECTIVE: To investigate the association between Anthrax Vaccine Adsorbed (AVA) received while on Active Duty and subsequent disability determined by the Veterans Benefits Administration. DESIGN, SETTING AND PARTICIPANTS: Case-control study nested in the cohort of all Active Duty personnel known to have separated from the US Army between December 1, 1997 and December 31, 2005. Cases were ≥10% disabled, determined either by the Army prior to separation (N=5846) or by the Veterans Benefits Administration (VBA) after separation (N=148,934). Controls (N=937,705) separated from the Army without disability, and were not receiving pensions from the VBA as of April 2007. Data were from the Total Army Injury and Health Outcomes Database and the VBA Compensation and Pension and Benefits database. MAIN OUTCOMES: Disability status (yes/no); for primary disability, percent disabled (≥10%, 20%, >20%) and type of disability. RESULTS: Vaccination against anthrax was four times more likely among disabled Veterans with hostile fire pay records (HFP, a surrogate for deployment). Vaccinated Soldiers with HFP had lower odds of disability separation from the Army 0.89 (0.80, 0.98); there was no association between vaccine and receiving Army disability benefits among those without HFP (OR=1.05, CI: 0.96, 1.14). Vaccination was negatively associated with receiving VA disability benefits for those with HFP (OR=0.66, CI: 0.65, 0.67), but there was little or no association between vaccine and receipt of VA disability benefits for those without HFP (OR=0.95, CI: 0.93, 0.97). CONCLUSIONS: Risk of disability separation from the Army and receipt of disability compensation from the VA were not increased in association with prior exposure to AVA. This study provides evidence that vaccination against anthrax is not associated with long term disability.

Risk of disability for US army personnel vaccinated against anthrax, 1998-2005.

To evaluate the potential for long-term or delayed onset health effects, we extended a previous cohort study of disability separation from the army associated with vaccination against anthrax. Analyses included stratified Cox proportional hazards and multiple logistic regression models. Forty-one percent of 1,001,546 soldiers received at least one anthrax vaccination; 5.21% were evaluated for disability. No consistent patterns or statistically significant differences in risk of disability evaluation, disability determination, or reason for disability were associated with anthrax vaccination. There was a dose-related trend in risk of disability for soldiers with 2 years' service, limited to those entering service in 2000 or later. Divergent patterns in risk suggest confounding by temporal or occupational risks of disability.

Effectiveness of an external ankle brace in reducing parachuting-related ankle injuries.

Outside-the-boot parachute ankle braces (PABs) worn during US Army paratrooper training have been shown to reduce the risk of severe ankle injuries. In spite of evidence to the contrary, anecdotal reports continue to suggest increases in risk of other types of injury, and the cost of obtaining and periodically replacing the PAB has been used to justify its discontinued use. The authors identified inpatient and outpatient treatment for injuries during US Army paratrooper training. Those undergoing training during two periods when PAB use was mandated had 40% lower risks of ankle injury (brace I, RR=0.60 (95% CI 0.47 to 0.75); brace II, RR=0.62 (95% CI 0.49 to 0.78)), with no difference in risks of other types of injury. There were no differences in risk of ankle injury during periods when brace use was not mandated. The PAB is safe, effective and cost effective.

Mortality in the German porcelain industry 1985-2005: first results of an epidemiological cohort study.

OBJECTIVES: To evaluate mortality due to lung cancer, silicosis, renal cancer, renal disease and other causes among German porcelain production workers potentially exposed to crystalline silica. METHODS: Seventeen thousand six hundred forty-four medical surveillance participants (1985-1987) were followed through 2005 for mortality. Cause-specific Standardized Mortality Ratios (SMR) and 95% confidence intervals were estimated. RESULTS: Women (SMR = 0.85; 95% CI = 0.78 to 0.93), but not men, demonstrated a healthy worker effect. Lung and renal cancers, and renal disease (non-malignant renal disease) were not associated with employment or exposure surrogates. Mortality was increased from silicosis (SMR = 7.20; 95% CI = 2.32 to 16.8) liver (SMR = 1.99; 95% CI = 1.29 to 2.93) and pancreatic (SMR = 1.71; 95% CI = 1.18 to 2.41) cancers among men, and diabetes among women (SMR = 1.74; 95% CI = 1.07 to 2.65). A sub-cohort of Bavarian workers generated similar but generally higher SMRs. CONCLUSIONS: Silicosis mortality was increased in this, among the largest studies to date. However, associations previously observed between crystalline silica exposure and renal or lung cancers or non-malignant renal disease were not supported.

Prolonged acute mechanical ventilation, hospital resource utilization, and mortality in the United States.

OBJECTIVE: Adjusted costs of mechanical ventilation (MV) are $1,500 per patient-day. We compared the prevalence, characteristics, and outcomes of MV < 96 hrs (MV < 96) and prolonged acute MV (PAMV) of > or = 96 hrs' duration in a representative sample of U.S. hospital discharges. DESIGN: A multicenter cross-sectional study. SETTING: Nationally representative sample of U.S. hospital discharges. PATIENTS: Adult hospital discharges were identified from the 2003 Nationwide Inpatient Sample, Healthcare Cost and Utilization Project from the Agency for Healthcare Research and Quality (AHRQ). PAMV was based on the presence of ICD-9 code 96.72, and MV < 96 hrs based on ICD-9 codes 96.70 and 96.71. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Of 31,340,578 discharges for adults (> or = 18 yrs), 2.4% had any MV, of which 469,168 (61%) had MV < 96, and 294,333 (39%) had PAMV. Patient demographics were similar for MV < 96 and PAMV. With the exception of acute myocardial infarction and chronic and end-stage renal disease without dialysis, the prevalence of coexisting conditions was higher in the PAMV group. Median length of stay (17 vs. 6 days) and hospital costs ($40,903 vs. $13,434) also were higher with PAMV vs. MV < 96. Although Agency for Healthcare Research and Quality disease severity and mortality probability were higher in the PAMV than MV < 96 group, actual mortality was similar between the two groups (34% vs. 35%). CONCLUSIONS: There were nearly 300,000 PAMV discharges in the United States in 2003 at an annual aggregated hospital cost of > $16 billion, or nearly two thirds of the cost for all of the MV discharges. Despite a higher predicted mortality, patients requiring PAMV had the same likelihood of being discharged alive as those on shorter-term MV. These analyses will help inform health care decision-making and resource planning in the face of an aging population.

Clinical epidemiological study of employees exposed to surfactant blend containing perfluorononanoic acid.

INTRODUCTION: An epidemiological study was conducted of a perfluorononanoic acid (PFNA) surfactant blend, to investigate whether clinical differences were apparent between employees who were potentially exposed to the surfactant and those who were not exposed. The surfactant blend, which is related to other previously studied perfluorinated materials, is used in the production of some high-performance polymers. METHODS: All 630 individuals employed at a polymer production facility using PFNA (CAS No 72968-38-8) at any time between 1 January 1989 and 1 July 2003 were included in the cohort. Plausibly related laboratory test results were abstracted from annual medical examination records, including liver enzyme function and blood lipids. Detailed work histories, available for all employees, provided the basis for determining exposure category. Thirty two clinical parameters were evaluated by exposure level at five points in time, determined to reflect changes in possible exposure intensity, as well as greatest number of records available. Annual cross-sectional analyses and longitudinal analyses that accounted for multiple measurements per person were conducted separately for men and women, by exposure groups. RESULTS: Differences by exposure group for all laboratory measures, adjusted for age and body mass index, were small and not clinically significant. Although some statistically significant pair-wise differences were observed, these observations were not consistent between men and women, or over the five analysis windows. For the seven outcome variables (liver enzymes and blood lipids) examined in separate longitudinal models, no significant increase or decrease was observed by unit increase in cumulative exposure intensity score. CONCLUSION: This is the first epidemiological study investigating the possible health effects in humans associated with exposure to PFNA blend. Based on laboratory measures assessed over more than a decade, no adverse clinical effects were detected from occupational exposure to PFNA blend.

A cohort mortality study of employees in the U.S. carbon black industry.

OBJECTIVES: The objectives of this study are to evaluate historical mortality patterns, especially due to cancers, among employees of the U.S. carbon black industry and to address the methodological shortcomings of previous U.S. mortality studies. METHODS: We followed mortality of 5011 workers employed 1 year or more since the 1930s at 18 carbon black facilities through December 31, 2003. Age-, race-, sex-, and calendar year-adjusted standardized mortality ratios (SMRs) were calculated using state-specific mortality rates. RESULTS: Follow up was 96% complete. All-cause (SMR = 0.74, 95% confidence interval [CI] = 0.70-0.78) and all-cancer mortality (SMR = 0.83, 95% CI = 0.74-0.92) showed significant deficits. No excess was observed from lung (SMR = 0.97, 95% CI = 0.82-1.15) or bladder (SMR = 0.93, 95% CI = 0.47-1.87) cancers or from nonmalignant respiratory diseases (SMR = 0.99, 95% CI = 0.83-1.18). No trends were seen with duration of employment or time since hire for any cause of death. CONCLUSION: Employment in carbon black production in the United States seems not to be associated with increased mortality overall, cancer overall and, in particular, lung cancer. Further research, however, incorporating a detailed exposure assessment is needed to determine whether exposure to carbon black at high levels may be associated with an increased risk of cancer.

Lung cancer mortality in the German chromate industry, 1958 to 1998.

OBJECTIVES: We conducted a mortality study of two German chromate production facilities and evaluated possible dose-response relationships between hexavalent chromium exposure and lung cancer. METHODS: Mortality was followed-up through 1998 and limited to those employed since each plant converted to a no-lime production process. More than 12,000 urinalysis results of chromium levels were available, as was smoking information. RESULTS: All-cause mortality indicated a healthy worker effect (standardized mortality ratio [SMR] = 0.80, 95% confidence interval [CI] = 0.67-0.96); however, lung cancers appeared to be increased (SMR = 1.48, 95% CI = 0.93-2.25). No clear dose-response was found in stratified analyses by duration of employment and time since hire. On the basis of urinary chromium data, lung cancer risk was elevated only in the highest exposure group (SMR = 2.09, 95% CI = 1.08-3.65). CONCLUSIONS: These data suggest a possible threshold effect of occupational hexavalent chromium exposure on lung cancer.

Low-level hexavalent chromium exposure and rate of mortality among US chromate production employees.

OBJECTIVE: Although numerous studies have reported an elevated lung cancer risk among chromium chemical production employees, few studies have focused on employees hired after major process changes and enhanced industrial hygiene controls were implemented. METHODS: This study examines the mortality experience of two post-change cohorts of chromate production employees constituting the current US chromium chemical industry. RESULTS: Mortality among chromium chemical workers generally was lower than expected on the basis of national and state-specific referent populations. Lung cancer mortality was 16% lower than expected, with only three lung cancer deaths (3.59 expected). CONCLUSION: The absence of an elevated lung cancer risk may be a favorable reflection of the post-change environment. However, longer follow-up allowing an appropriate latency for the entire cohort will be needed to confirm this conclusion.

Evaluation of the exposure-response relationship of lung cancer mortality and occupational exposure to hexavalent chromium based on published epidemiological data.

Some have suggested a threshold mechanism for the carcinogenicity of exposure to hexavalent chromium, Cr(VI). We evaluated the nature of the exposure-response relationship between occupational exposure to Cr(VI) and respiratory cancer based on results of two recently published epidemiological cohort studies. The combined cohort comprised a total of 2,849 workers employed at two U.S. chromate production plants between 1940 and 1974. Standardized mortality ratios (SMRs) for lung cancer in relation to cumulative Cr(VI) exposure categories were reported using regional mortality rates. Linear additive and multiplicative relative risk regression models were fit to the SMRs of the individual and combined studies. Both models fit the data from the individual studies reasonably well; however, the fit was somewhat less adequate for the pooled data. Meta-analysis of the slope estimates obtained from the multiplicative relative risk model showed substantial heterogeneity between the two epidemiological studies. In conclusion, these data indicate that a linear dose response describes the relationship between Cr(VI) and lung cancer reasonably well, and therefore these analyses do not necessarily support the threshold hypothesis for the lung carcinogenicity of Cr(VI). However, these results must be interpreted with recognition of the limitations of the use of epidemiological data in the evaluation of nonlinear exposure-response patterns.

Dose-response and risk assessment of airborne hexavalent chromium and lung cancer mortality.

This study evaluates the dose-response relationship for inhalation exposure to hexavalent chromium [Cr(VI)] and lung cancer mortality for workers of a chromate production facility, and provides estimates of the carcinogenic potency. The data were analyzed using relative risk and additive risk dose-response models implemented with both Poisson and Cox regression. Potential confounding by birth cohort and smoking prevalence were also assessed. Lifetime cumulative exposure and highest monthly exposure were the dose metrics evaluated. The estimated lifetime additional risk of lung cancer mortality associated with 45 years of occupational exposure to 1 microg/m3 Cr(VI) (occupational exposure unit risk) was 0.00205 (90%CI: 0.00134, 0.00291) for the relative risk model and 0.00216 (90%CI: 0.00143, 0.00302) for the additive risk model assuming a linear dose response for cumulative exposure with a five-year lag. Extrapolating these findings to a continuous (e.g., environmental) exposure scenario yielded an environmental unit risk of 0.00978 (90%CI: 0.00640, 0.0138) for the relative risk model [e.g., a cancer slope factor of 34 (mg/kg-day)-1] and 0.0125 (90%CI: 0.00833, 0.0175) for the additive risk model. The relative risk model is preferred because it is more consistent with the expected trend for lung cancer risk with age. Based on statistical tests for exposure-related trend, there was no statistically significant increased lung cancer risk below lifetime cumulative occupational exposures of 1.0 mg-yr/m3, and no excess risk for workers whose highest average monthly exposure did not exceed the current Permissible Exposure Limit (52 microg/m3). It is acknowledged that this study had limited power to detect increases at these low exposure levels. These cancer potency estimates are comparable to those developed by U.S. regulatory agencies and should be useful for assessing the potential cancer hazard associated with inhaled Cr(VI).

Cause-specific mortality among Kelly Air Force Base civilian employees, 1981-2001.

In response to concerns about occupational and environmental exposures, and a perceived cluster of amyotrophic lateral sclerosis (ALS) in the community, the mortality experience among 31,811 civilian employees who worked for at least 1 year between 1981 and 2000 at Kelly Air Force Base, Texas was ascertained. A total of 3264 deaths occurred through October 31, 2001. Overall, significant deficits in mortality were observed for all causes of death and all cancers combined. An excess of breast cancer [standardized mortality ratio (SMR) = 216; 95% confidence interval (CI) = 128-341] among blue-collar women was identified, and remained elevated after adjusting for race and ethnicity [rate ratio (RR) = 2.83; 95% CI = 1.50-5.34]. Mortality from motor neuron disease, which includes ALS deaths, was not increased overall (SMR = 0.98; 95% CI = 0.52-1.68), and was lower among blue-collar employees and higher among white-collar employees than expected, based on small numbers. Overall, mortality patterns indicated a healthy worker population and no large increased mortality associated with employment at Kelly Air Force Base.