D. Alan Nelson

Sickle Cell Trait, Rhabdomyolysis, and Mortality among U.S. Army Soldiers

BACKGROUND Studies have suggested that sickle cell trait elevates the risks of exertional rhabdomyolysis and death. We conducted a study of sickle cell trait in relation to these outcomes, controlling for known risk factors for exertional rhabdomyolysis, in a large population of active persons who had undergone laboratory tests for hemoglobin AS (HbAS) and who were subject to exertional-injury precautions. METHODS We used Cox proportional-hazards models to test whether the risks of exertional rhabdomyolysis and death varied according to sickle cell trait status among 47,944 black soldiers who had undergone testing for HbAS and who were on active duty in the U.S. Army between January 2011 and December 2014. We used the Stanford Military Data Repository, which contains comprehensive medical and administrative data on all active-duty soldiers. RESULTS There was no significant difference in the risk of death among soldiers with sickle cell trait, as compared with those without the trait (hazard ratio, 0.99; 95% confidence interval [CI], 0.46 to 2.13; P=0.97), but the trait was associated with a significantly higher adjusted risk of exertional rhabdomyolysis (hazard ratio, 1.54; 95% CI, 1.12 to 2.12; P=0.008). This effect was similar in magnitude to that associated with tobacco use, as compared with no use (hazard ratio, 1.54; 95% CI, 1.23 to 1.94; P<0.001), and to that associated with having a body-mass index (BMI; the weight in kilograms divided by the square of the height in meters) of 30.0 or more, as compared with a BMI of less than 25.0 (hazard ratio, 1.39; 95% CI, 1.04 to 1.86; P=0.03). The effect was less than that associated with recent use of a statin, as compared with no use (hazard ratio, 2.89; 95% CI, 1.51 to 5.55; P=0.001), or an antipsychotic agent (hazard ratio, 3.02; 95% CI, 1.34 to 6.82; P=0.008). CONCLUSIONS Sickle cell trait was not associated with a higher risk of death than absence of the trait, but it was associated with a significantly higher risk of exertional rhabdomyolysis. (Funded by the National Heart, Lung, and Blood Institute and the Uniformed Services University of the Health Sciences.).

Long-Acting Reversible Contraceptive Placement Among Active-Duty U.S. Army Servicewomen

OBJECTIVE To quantify uptake of long-acting reversible contraceptives (LARC)-intrauterine devices (IUDs) and hormonal implants-among U.S. Army active-duty female soldiers and identify characteristics associated with uptake. METHODS This retrospective cohort study used the Stanford Military Data Repository, which includes all digitally recorded health encounters for active-duty U.S. Army soldiers from 2011 to 2014. We analyzed data from women aged 18-44 years to assess rates of LARC initiation using medical billing codes. We then evaluated predictors of LARC initiation using multivariable regression. RESULTS Among 114,661 servicewomen, 14.5% received a LARC method; among those, 60% received an IUD. Intrauterine device insertions decreased over the study period (38.7-35.9 insertions per 1,000 women per year, β=0.14, 95% confidence interval [CI] -0.23 to -0.05, P<.05), whereas LARC uptake increased, driven by an increase in implant insertions (20.3-35.4/1,000 women per year, β=0.41, CI 0.33-0.48, P<.001). Younger age was a positive predictor of LARC uptake: 32.4% of IUD users and 62.6% of implant users were in the youngest age category (18-22 years) compared with 9.6% and 2.0% in the oldest (36-44 years). The likelihood of uptake among the youngest women (compared with oldest) was most marked for implants (adjusted relative risk 7.12, CI 5.92-8.55; P<.001). A total of 26.2% of IUD users had one child compared with 13.2% among non-LARC users (adjusted relative risk 1.94, CI 1.85-2.04, P<.001). The majority (52.2%) of those initiating IUDs were married, which was predictive of uptake over never-married women (adjusted relative risk 1.52, CI 1.44-1.59, P<.001). CONCLUSION Among servicewomen, we observed low but rising rates of LARC insertion, driven by increasing implant use. Unmarried and childless soldiers were less likely to initiate LARC. These findings are consistent with potential underutilization and a need for education about LARC safety and reversibility in a population facing unique consequences for unintended pregnancies.

Prediction of all-cause occupational disability among US Army soldiers

Introduction Long-term occupational disability rates associated with eventual discharges from military service have risen sharply among active-duty US Army soldiers during the last three decades, with important implications for soldier health and national security alike. To address this problem, we built predictive models for long-term, all-cause occupational disability and identified disability risk factors using a very large, multisource database on the total active-duty US Army. Methods We conducted a cross-temporal retrospective cohort study and used mixed-effects logistic regression models to derive and validate disability risk assignments. The derivation cohort included 510 616 US Army soldiers on duty in December 2012, and the validation cohort included 483 197 soldiers on duty in December 2013. Results The predictive model yielded an overall c-statistic of 85.97% (95% CI 85.61% to 86.32%). Risk thresholds at the populations 75th and 95th centiles identified 80.53% and 42.08%, respectively, of the disability designations that occurred population wide during the subsequent 9 months. Frequent work excusals, high outpatient care utilisation and psychotropic medication use were the strongest independent predictors of later disability. Conclusions These findings indicate that predictive models using diverse data types can successfully anticipate long-term occupational disability among US Army soldiers and could be used for disability risk screening.

Deployment and Preterm Birth Among US Army Soldiers

With increasing integration of women into combat roles in the US military, it is critical to determine whether deployment, which entails unique stressors and exposures, is associated with adverse reproductive outcomes. Few studies have examined whether deployment increases the risk of preterm birth; no studies (to our knowledge) have examined a recent cohort of servicewomen. We therefore used linked medical and administrative data from the Stanford Military Data Repository for all US Army soldiers with deliveries between 2011 and 2014 to estimate the associations of prior deployment, recency of deployment, and posttraumatic stress disorder with spontaneous preterm birth (SPB), adjusting for sociodemographic, military-service, and health-related factors. Of 12,877 deliveries, 6.1% were SPBs. The prevalence was doubled (11.7%) among soldiers who delivered within 6 months of their return from deployment. Multivariable discrete-time logistic regression models indicated that delivering within 6 months of return from deployment was strongly associated with SPB (adjusted odds ratio = 2.1, 95% confidence interval: 1.5, 2.9). Neither multiple past deployments nor posttraumatic stress disorder was significantly associated with SPB. Within this cohort, timing of pregnancy in relation to deployment was identified as a novel risk factor for SPB. Increased focus on servicewomens pregnancy timing and predeployment access to reproductive counseling and effective contraception is warranted.

Exertional Heat Illness in the Military: Risk Mitigation

This chapter focuses on exertional heat illness (EHI) in the military and covers common scenarios of EHI, the epidemiology, and guidelines related to risk mitigation and physical activity modifications. EHI risk is particularly high among new military recruits and those in combat occupational specialties. Other extrinsic and intrinsic factors are reviewed, including sickle cell trait and medications, which have received more attention recently. Military leaders are responsible for mitigating EHI risk at both the unit and individual level. The five steps of risk management are identify hazards, assess hazards, develop controls and make risk decisions, implement controls, and supervise and evaluate. Each step is discussed and elucidated with examples of work/rest hydration cycles by heat categories and Army risk management matrices. Military leaders need to remain vigilant and adapt risk management strategies; as the military’s demographic/occupational makeup changes, the evidence base for EHI risk mitigation evolves, and new technologies become available.

Stated Pain Levels, Opioid Prescription Volume, and Chronic Opioid Use Among United States Army Soldiers

Introduction The use of opioids has increased drastically over the past few years and decades. As a result, concerns have mounted over serious outcomes associated with chronic opioid use (COU), including dependency and death. A greater understanding of the factors that are associated with COU will be critical if prescribers are to navigate potentially competing objectives to provide compassionate care, while reducing the overall opioid use problem. In this study, we study pain levels and opioid prescription volumes and their effects on the risk of COU. This study leveraged passive data sources that support automated decision support systems (DSSs) currently employed in a large military population. The models presented compute monthly, person-specific, adjusted probability of subsequent COT and could potentially provide critical decision support for clinicians engaged in pain management. Materials and Methods The study population included all outpatient presentations at military medical facilities worldwide among active duty United States Army soldiers during July 2011 to September 2014 (17,664,006 encounters; population N = 552,193). We conducted a retrospective cohort study of this population and employed longitudinal data and a discrete time multivariable logistic regression model to compute COT probability scores. The contribution of pain scores and opioid prescription quantities to the probability of COT represented analytic foci. Results There were 13,891 subjects (2.5%) who experienced incident COT during the observed time period. Statistically significant interactions between pain scores and prescription quantity were present, in addition to effects of multiple other control variables. Counts of monthly opioid prescriptions and maximum stated pain scores per month were each positively associated with COT. A wide range in individual COT risk scores was evident. The effect of prescription volume on the COT risk was larger than the effect of the pain score, and the combined effect of larger pain scores and increased prescription quantity was moderated by the interaction term. Conclusions The results verified that passive data on the US Army can support a robust COT risk computation in this population. The individual, adjusted risk level requires statistical analyses to be fully understood. Because the same data sources drive current military DSSs, this work provides the potential basis for new, evidence-based decision support resources for military clinicians. The strong, independent impact of increasing opioid prescription counts on the COT risk reinforces the importance of exploring alternatives to opioids in pain management planning. It suggests that changing provider behavior through enhanced decision support could help reduce COT rates.

Gender differences in the associations of body mass index, physical fitness and tobacco use with lower extremity musculoskeletal injuries among new US Army soldiers

Background Musculoskeletal (MSK) injuries are a leading cause of morbidity among US Army soldiers, especially among women and the newly enlisted. While extremes of body mass index (BMI), low physical fitness and tobacco use have been identified as risk factors, no prior studies have determined the combined effects of these risk factors or tested for gender differences in the associations. Methods We conducted a retrospective cohort study utilising the Stanford Military Data Repository to study all enlisted soldier accessions to the US Army between January 2011 and January 2014, with follow-up through December 2014 (n=238 772). We used discrete-time logistic regression to test for associations between demographic, socioeconomic and health behaviour-related predictors and incident lower extremity injuries. We included interaction terms to test for gender differences. Results Among men, there were greater adjusted odds of injury among underweight (OR 1.27), overweight (OR 1.14) and obese soldiers (OR 1.54) (all p<0.001) relative to normal-weight soldiers. No statistically significant differences in the odds of injury on the basis of BMI were observed for female soldiers. Physical fitness was a significantly stronger predictor of injury for female as compared with male soldiers, while the association between tobacco use and injury was stronger for men (OR 1.47) than for women (OR 1.30) (p<0.001 for both). Conclusion This is the largest known study to simultaneously assess important, modifiable musculoskeletal injury risk factors and to test for gender differences in these associations. These findings provide critical gender-related nuances for clinicians and leaders seeking to reduce the risk of these problems.

Sickle Cell Trait and Heat Injury Among US Army Soldiers

There is concern that sickle cell trait (SCT) increases risk of exertional collapse, a primary cause of which is heat injury. However, to our knowledge, no population-based studies among active individuals have addressed this, representing a critical evidence gap. We conducted a retrospective cohort study of SCT-tested African-American soldiers who were on active duty in the US Army anytime between January 2011 and December 2014. Using Cox proportional hazards models and adjusting for demographic and medical factors, we observed no significant associations between SCT and either mild heat injury (hazard ratio (HR) = 1.15, 95% confidence interval (CI): 0.84, 1.56; n = 45,999) or heat stroke (HR = 1.11, 95% CI: 0.44, 2.79; n = 46,183). Risk of mild heat injury was substantially higher among soldiers with recent prescriptions for antipsychotic agents (HR = 3.25, 95% CI: 1.33, 7.90). Risk of heat stroke was elevated among those with a prior mild heat injury (HR = 17.7, 95% CI: 8.50, 36.7) and among overweight and obese individuals (HR = 2.91 (95% CI: 1.38, 6.17) and HR = 4.04 (95% CI: 1.72, 9.45), respectively). In a setting where universal precautions are utilized to mitigate risk of exertion-related illnesses, SCT is not associated with either mild heat injury or heat stroke.

Prior depression and incident back pain among military registered nurses: A retrospective cohort study

BACKGROUND Occupational back pain rates are substantial among registered nurses, and nurses also report high rates of depression. The role of depression as a potential predictor of back pain among nurses appears understudied. OBJECTIVES The objective of the study was to determine whether a history of depression predicted incident back pain in a population of military registered nurses when controlling for relevant risk factors. DESIGN We employed a retrospective cohort approach using longitudinal data in which gender-specific subject groups were followed from the beginning of duty as a registered nurse to the occurrence of an outcome, or to censoring due to completion of service or the end of available data. PARTICIPANTS This study included all United States Army registered nurses who began work during 2011-2014 without evidence of prior back pain in clinical records. METHODS Data from automatically-collected medical and administrative sources were combined and used to provide 2134 person-years of observation on 1248 individuals. These data were organized at the person-month level in a panel data structure to support discrete-time multivariable logistic regression models. The models examined the relationships between prior depression, Body Mass Index, the presence of prior combat duty and selected control variables and the outcome, the incident occurrence of back pain. RESULTS The incidence rate of back pain was 18.6 per 100 person-years and the period prevalence was 31.7%. Prior depression was a statistically-significant predictor of incident back pain among female subjects (odds ratio [OR]: 1.75, 95% confidence interval [CI]: 1.08-2.83, P-value<0.05). Body Mass Index of 30kg/m2 or greater, prior combat deployments, and age 36 years or older was each associated with back pain for male and female nurses. CONCLUSIONS The studys findings provide the first evidence of a temporal link between antecedent depression and later back pain among female military nurses. High Body Mass Index was found to be a further, modifiable risk factor for back pain in this population.

Objective Effects of Breast Reduction Surgery on Physical Fitness

Background Reduction mammaplasty is known for excellent outcomes and patient satisfaction. Although patients report improvements in pain, weight loss, and exercise levels, objective data on physical fitness benefits are limited. Methods Using the Stanford Military Data Repository, we identified 89 US Army active duty women with at least 1 pre- and postoperative Army Physical Fitness Test (APFT) who underwent reduction mammaplasty during 2011 to 2014. We used paired t tests to compare pre- and postoperative APFT score means and raw values for push-ups, sit-ups, and the 2-mile run. Results There were 56 subjects (62.9%) who improved in total APFT scores. Total score means increased from 235.9 preoperatively to 243.4 postoperatively (P = 0.0065). Of 28 subjects with at least 2 APFT scores before and after surgery, 20 (71.4%) improved in total scores. The subgroups mean total score increased from 237.8 to 251.3 (P = 0.0009). Comparing individual pre- and postprocedure APFTs, all subjects demonstrated a mean 3.9% (SD, 0.1) improvement in total scores, and the subpopulation of 28 improved by 6.3% (SD, 0.1). In all events, mean performance values trended toward better postoperative scores. Differences were statistically significant for the total population for the number of sit-ups (P = 0.035), and, for the subgroup of 28, differences were statistically significant for the total score (P = 0.0009), sit-ups (P = 0.0002), and push-ups (P = 0.0134). Conclusions Reduction mammaplasty was associated with postoperative physical fitness improvements among US Army active duty women. Soldier data are useful for objectively assessing physical fitness effects of breast reduction surgery.