Appendix H: The Keokuk County Rural Health Study Final Report
Keokuk County Rural Health Study: The Epidemiology of Agricultural Diseases and Injuries
Grant Number: # 5 U50 OH 007848
James A. Merchant, MD, DrPH, Project Investigator
Final Progress Report
- Project Narrative
The Keokuk County Rural Health Study (KCRHS) is a population-based, prospective study of health status and environmental exposures of a large stratified random sample of residents in one rural Iowa county. The study focuses on injury and respiratory disease and monitors health care delivery, geriatric health, mental health, and other health outcomes, as well as behavioral risk factors for disease and injury. Injury and disease prevalence is investigated in relation to occupational, agricultural, and other environmental exposures. The specific aims of the KCRHS have from its inception has focused on serial cross-sectional and prospective evaluations of rural/agriculturally-related respiratory diseases and rural/agriculturally-related injuries, and their respective risk factors–especially those risk factors related to the rural and agricultural environment. In addition to the two primary aims, the KCRHS has assessed other important agriculturally-related health outcomes and associated risk factors, including specific agricultural occupational and environmental exposures, hearing loss, vision, mental and neurobehavioral health, and rural health services.
The population at risk and sampling unit is the household—the entire farm family, as the family unit shares agricultural and rural environmental, as well as genetic, risk factors, and because very little research is available ohn agricultural health outcomes among farm women and children. Although the sampling unit was the household, each member of a selected household was invited to participate in the study provided they lived in the house 50% of the time. KCRHS enrolled 1004 households (2284 individuals) during Round 1 (1994 to 1998), 1002 households (2163 individuals) in Round 2 (1999 to 2004) and concluded with Round 3 (2006-2011; 662 households, 1253 individuals). Participants range in age from newborn to 98 years of age and are about equally divided between males and females. The families live in farm, rural nonfarm, and town households, representing men, women, and children, the elderly, farmers, and nonfarmers. Although the sample is stratified by residence type, the entire county is, by definition, rural, because the largest town has fewer than 2500 residents.
- Specific Aims and Outputs
The KCRHS has encompassed all NIOSH National Occupational Research Agenda (NORA) 1 priorities for diseases and injuries, with few exceptions, for all three rounds (allergic and irritant dermatitis, asthma and chronic lung disease, fertility and pregnancy abnormalities (Round 1 and 2 only), hearing loss, infectious diseases (Round 2), low back disorders, musculoskeletal disorders, and trauma); all NORA 1 work environment and work force priorities (indoor environment, mixed exposures, organization of work, and special populations at risk); and all NORA 1 research tools and approaches (control technology and personal protective equipment, exposure assessment methods, health services research, and social and economic consequences of workplace illness and injury). The KCRHS has also embraced all NORA 2 Agricultural, Forestry, and Fishing Agenda strategic goals for all three rounds (surveillance, vulnerable populations, outreach/partnerships/communications, agricultural safety and agricultural health). In addition, the KCRHS has included, or facilitated through related funding, all National Research Council (NRC) program characteristics for “the ideal NIOSH Agricultural, Forestry, and Fishing Research Program,” including: 1) identification and characterization of injuries and illness and detailed characterization of populations at risk through surveillance, 2) identification and characterization of special populations and unique health and safety risks they face; 3) identification and characterization of health effects associated with chemical, physical, and biological agents encountered in agriculture, fishing and forestry; 4) identification, development, evaluation, and implementation of control systems to reduce injury and illness; and 5) development of efficient and effective outreach mechanisms for dissemination and delivery of knowledge developed through research (http://www.nap.edu/catalog.php?rrecord_id=12088).
Appendix A provides a summary of support provided by the KCRHS in education and training, research collaborations, support for sponsored research, and for questionnaire and data sharing:
- Post-doctoral fellows—6
- Graduate student degree support—17
- Fogarty Scholar Trainees—5
- Research collaborations with organizations—24
- Research collaborations with individuals—51
- Sponsored research using KCRHS data or research subjects—24
- Sharing full KCRHS questionnaire module questionnaires—5, plus many more individual questionnaire modules
Summary of published research by Specific Aim:
Specific Aim 1: To assess the association between observed risk factors and injuries through prospective studies of participants in Round 2 and 3. Agricultural and rural injury research has been a primary specific aim of the KCRHS from the outset of this study, and has well been documented in multiple publications from Round 1 data (Zwerling et al, 1997; Nordstrom et al, 2000; Nordstrom et al, 2001a,b; Zwerling et al, 2001; Merchant et al, 2002; Nordstrom et al, 2003; Murty et al, 2003; Peek-Asa et al, 2005a,b). These citations documented population-based, rural and agricultural risk factors and injury outcomes among family members, firearm use risk factors, unintentional rural adult injuries, non-fatal childhood injury risk factors, emotional and physical partner abuse, and rural fire risk factors. For example, Daly et al (2007) reported the first population-based study of rural elder domestic partner violence from Round 1 data, finding 2% of cohabiting elderly adults reported physical abuse and 32% emotional abuse. Emotional abuse risk factors included having depressive symptoms, higher antisocial personality scores, and living on a farm or rural non-farm, rather than in town. In a recent published study, Renner et al. (2014) found a strong co-occurrence of victimization and perpetration of both physical and emotional intimate partner violence, and that couples with IPV histories were 2-3 times more likely to display depressive symptoms that those without abusive histories. The impact of parental physical violence on academic performance among children witnessing parental violence was examined using Iowa Tests of Basic Skills data obtained during the Round 1 study period Peek-Asa et al (2007). Children witnessing parental violence performed an average of 12.2 percentile points lower than children without parental violence, and larger test score reductions among girls and among children less than 12 years old. Parental violence was found to be less common among farm partners than town or rural non-farm partners. Yang et al (2006), based on a survey sample of Round 1 participants, documented that 57% of KC households reported having a fire escape plan, that households with children were more likely to have a plan, but that households with elderly or disabled family members were less likely to have or practice an escape plan, thus suggesting the need for alternate injury prevention strategies for these higher risk households. Peek-Asa et al (2005), from the same survey data, assessed compliance with National Fire Protection Association guidance and found that only one in five KCRHS homes were in compliance with NFPA guidance, and that was therefore a need for greater awareness of these guidelines, how to install, and how to maintain fire alarms in rural communities. These baseline studies led to the first rural randomized control trial of smoke alarms, which found that lithium batteries and photoelectric alarms were more expensive than alternatives, but that the added financial investment may be more worthwhile in terms of overall performance (Yang, et al, 2008). Additional manuscripts focused on intimate partner and youth violence are currently in review (Renner et al., Journal of Family Violence) and in preparation (Harland et al.; Frederick & Ramirez; Schwab-Reese et al.).
Specific Aim 2: To assess the association between observed risk factors and mental health/ neurobehavioral outcomes through prospective studies of participants of Round 2 and 3. Previously published data from Round 1 found no significant differences by household type for mental health outcomes, but did report that rural women had higher rates of depressive symptoms and had been less often treated for depression (Merchant et al, 2002). Also, suicide ideation among Round 1 participants (8.2%), was most strongly associated with depressive symptoms, alcohol use, infrequent social contact and financial loss, but found not to differ by household type (Turvey et al, 2002). Depressive symptoms, after controlling for other risk factors, were found to be a risk factor (RR=1.41) for unintentional injury (Tiesman et al, 2006). Sleep disturbance, which had been noted an associated finding in our previous reports on depression, were reported in three papers (Choi et al, 2006; Kohatsu et al, 2006; Hartz et al, 2006). Importantly, alcohol consumption of 1-2 or more drinks per day increased injury risk among those with sleep problems; however, having 7.5 hours or more of sleep per night was associated with fewer injuries (Choi et al, 2006). Self-reported sleep disturbance, after controlling for confounding risk factors, was also found to be associated with a higher body mass index (75% of farm men in Round 1 were overweight or obese, Merchant et al, 2002) among employed adults (Kohatsu, et al, 2006).
Specific Aim 3: To assess the association between observed risk factors and measures of respiratory disease through prospective studies of the participants in Round 2 and 3. Analysis of risk factors for respiratory disease from Round 1 data (Merchant et al, 2002) found that living in a rural residence was associated with an increase in chest wheeze with or without a cold. Furthermore and in contrast to many well documented agricultural respiratory exposures, having ever farmed or currently living on a farm was not associate with increases in respiratory symptoms; rather men in this study had significantly lower rates of attacks of wheezing and lower rates of a history of asthma or doctor diagnosed asthma, which we concluded may be attributable to selection or reporting bias, or both (Merchant et al, 2002). In contrast, in a KCRHS facilitated study, childhood asthma was found to be common (19%) and similar in prevalence to studies of childhood asthma in urban communities (Chrischilles et al, 2004). Also, one third of Round 1 children were found to have one or more of four indicators of childhood asthma (Merchant et al, 2005). Multivariate modeling, accounting for all other significant risk factors, found living on a swine farm that added antibiotics to feed was significantly associated with asthma/medication for wheeze, that 44% of children living on a swine farm reported one or more asthma indicators, and that 56% of children living on a swine farm which added antibiotics to feed reported one or more asthma outcomes. These and other community-based studies of asthma and other health outcomes in Iowa, North Carolina and Germany, are addressed in an Epidemiology commentary (Merchant, 2011). A nested case-control study from Round 1 data found an increase in prevalence of wheezing among farmers homozygous for CD14/-159T or CD14/-1619G (LeVan et al, 2005), suggesting genetic modulation of lung function and wheezing among agricultural workers, a hypothesis being pursued in Round 3, and in follow-up of Round 1 and 2 participants, through collection of DNA on as many KCRHS participants as possible. A serological study of KCRHS farmers (not limited to swine farmers), compared with veterinarians and meat processing workers, found significantly higher titers of H1N1 and H1N2 swine influenza among KCRHS farmer (OR=35.3), making clear that occupational farming exposures in KC increased farmers’ risk to infection with swine influenza virus, and therefore that livestock exposed farmers should be included in pandemic surveillance, immunization and antiviral strategies (Myers, et al, 2006). Finally, KCRHS investigators have played an important role in leading and participating in critical reviews of health effects data arising from exposures to from concentrated farm animal facilities (CAFOs), and in recommending research priorities and public policies (ISU/UI Study Group, 2002; Merchant et al, 2008; Pew Commission on Industrial Farm Animal Production, 2008; Merchant, 2011). The dose-response relationship between CAFO exposures and asthma among rural children has been documented from Round 2 data as part of a PhD dissertation (Pavilonis, 2013a).
Specific Aim 4: To assess the association between observed risk factors and hearing impairment through prospective studies of participants in Round 2 and 3. Noise induced hearing loss is well recognized among farmers who are frequently exposed to noise from farm equipment and livestock. However, assessment of hearing loss among KC farm adolescents found over 50% to have significant hearing loss, substantially higher than that among US children (12.5%, estimated from the 3rd National Health and Nutrition Survey-NHANES) (Mudipalli, 1999, thesis). A more recent study of KCRHS farm and other rural youth documented daily noise exposures to frequently exceed (44%) the NIOSH REL of 85 dBA, many of which were farming related (Humann et al, 2011). In rural KC, 85% all men work or have worked in farming operations, and well over half of KC women work or have worked in farming (Round 1). It was therefore, not surprising to find that hearing loss was common, but finding that 99% of all adults in the KCRHS to have hearing impairment (using a statistical definition, lower than 95th percentile of normal) was informative (Flamme et al, 2005). Notched configurations typical of noise-induced hearing loss were most common between the ages of 30-59, while hearing loss interfering with speech began to increase rapidly among men in the fourth decade and among women in the sixth decade. Further comparison of hearing impairment by gender and audiometric configuration between the KCRHS and NHANES during the same time period, found hearing impairments to be more common among KCRHS participants (Cilette and Flamme, 2008). Humann et al. (2012) examined Round 2 audiometric data for participants 18 years of age and older (n=1568) for associations with 12 agricultural activities. Using a broad and inclusive definition of farming (ever worked on a farm), statistically significant differences in the mean decibels of hearing loss and the prevalence of hearing loss >25dB were found between male farmers and male non-farmers, but only for the lower frequency pure tone averages (PTA). Except for working with livestock, no other agricultural-specific activity was associated with significant hearing loss outcomes. In a co-variate linear regression analysis, the interaction of years worked on a farm and age was significantly associated with all three PTA defined outcomes, and the interaction of years worked on a farm and male gender was significantly associated with the NIOSH defined PTA outcome.
Specific Aim 5: To assess the association between observed risk factors and visual impairment through prospective studies of participants in Round 2 and 3. Assessment of visual acuity, blindness and vision accommodation among adults in Round 1 of the KCRHS found bilateral blindness in 0.44% of the study population, a monocular blindness prevalence of 3.5%, and significant visual impairment in one of both eyes in 10.6%, and that nearly 19% of the population had visual problems not corrected by lenses or contacts. Farm adults were found to have less visual impairment in one or both eyes than rural non-farm or town household members, while rural non-farm adults had significantly greater impairment in the worst eye (Oprescu, 2006, thesis). Analysis of Round 2 vision data, injury incidence controlling for other injury risk factors is pending.
Specific Aim 6: To assess measures of the agricultural and rural environment for evaluation of selected disease and injury outcomes (Specific Aims 1-5) from Rounds 2 and 3. Assessment of environmental exposures in KC homes (Round 1) have documented multiple household and farm hazardous exposures, including questionnaire data finding 25% of tractors with ROPS and 39% with PTO shields (Reynolds et al, 1997; Reynolds et al, 1998; Taylor et al, 1999). Comparison of organic dust aerosols in enclosed swine production units informed prediction estimates of inhalable and total dust concentrations among CAFO workers (Taylor and Reynolds, 2001). Round 2 KCRHS data allowed characterization of agricultural tasks among farm youth, finding that 50% of adolescent boys worked 10 hours a week for one year-or for one month in farming, while nearly 20% of adolescent girls worked that much (Park et al, 2003). Occupational exposures to hazardous tasks were common, especially among adolescent boys. The age at which farm youth began to engage in hazardous work typically began between ages 10-12, with the mean age for riding as a second passage on a tractor much lower (8.6-8.9 depending on whether reported by the youth or their parent). In general, adolescent youth reported beginning hazardous farm work at lower estimated ages than ages estimated by their parents. A follow-up field survey of farm tractors on the 341 farms participating in Round 1, documented that 39% had ROPS, but that only 4% of farmer reported that their tractor had a seat belt and that they wore seat belts during operation (Sanderson et al, 2006). This study concluded that until there is a dramatic decrease in the number of tractors operated without ROPS or seatbelts, the annual US incidence of 120-130 tractor overturn deaths will persist. Reynolds et al (2007) reported exposures to agricultural chemical and use of personal protective equipment (PPE) among KCRHS participants completing occupational surveys, a third of whom reported lifetime use of farm chemicals. Use of personal protective equipment varied by chemical; however, the vast majority reported never using PPE during mixing or application. Also, there was no difference in use of PPE whether a pesticide application course had been completed, or not, suggesting the need for more effective training methods. A series of studies of pesticide contamination inside farm and non-farm homes documented important direct exposures to pesticides from farm tasks, but also that farm homes especially, are frequently contaminate with farm chemicals tracked into the home on farm clothing, thereby exposing farm women, children and other family members (Curwin et al, 2002; Curwin et al, 2005a,b; Curwin et al, 2006). A series of three publications on which his PhD dissertation was based, have been published by Brian Pavilonis (documenting dose-related CAFO exposures and childhood asthma, particulate exposures in rural air and rural homes and dosimeter measured exposure to hydrogen sulfide in relation to CAFOs and rural residences (Pavilonis et al, 2013 a, b, c).
- On-going research
With completion of Round 3, the KCRHS has transitioned to use of this rich dataset for further detailed analyses of specific rural/agricultural exposures, other risk factors and their associated health outcomes through initiated research grants under the direction of Drs. Merchant and Kelly and in collaboration with the College of Public Health Center for Public Health Statistics. In addition to the continuing involvement of University of Iowa faculty, staff and students, the project has on-going external research collaborations with:
- Dr. Paul Hennenberger and Dr. Michael Humann, Division of Respiratory Disease Studies, NIOSH, Morgantown, WV. This four year NORA grant is a product of the cooperative agreement between the GPCAH and DRDS–“Effect of Occupational Exposures on Spirometry in a Rural Population” KCRHS and NIOSH IRB and data-use agreements are submitted and possibly completed by NIOSH.
- Dr. Tricia D. LeVan Pulmonary, Critical Care, Sleep, and Allergy Division, Department of Internal Medicine and Department of Epidemiology, University of Nebraska Medical Center, Omaha, NE.
“Variation in Endotoxin Receptors and Their Association with COPD Phenotypes”, a GPCAH pilot project that will be extended to genotype the entire adult cohort for COPD genes will be funding by Dr. LeVan of the Department of Internal Medicine, but will be approved via our still valid KCRHS IRB and data-use agreements (will be modified from pilot project).
- Dr. David Schwartz, Department of Medicine, University of Colorado Denver, Aurora, CO
“Analysis of asthma phenotypes and genotypes”. This study will be funded through the Department of Internal Medicine (Schwartz, Head) in conjunction with epigenetic studies of urban populations. KCRHS IRB and data-set agreements are being completed.
- Chrischilles E. Ahrens R, Kuehl A, Kelly KM, Thorne P, Burmeister L, Merchant J. Asthma prevalence an morbidity among rural Iowa school children. J Allergy Clin Immunol, 113(1):66-71, 2004.
- Choi S-W, Peek-Asa C, Sprince NL, Rautiainen RH, Flamme GA, Whitten PS, Zwerling C. Sleep quantity and quality as a predictor of injuries in a rural population. American Journal of Emergency Medicine. 2006;24(2):189-96.
- Ciletti, L., Flamme, G.A. Prevalence of hearing impairment by gender and audiometric configuration: Results from the National Health and Nutrition Examination Survey (1999-2004) and the Keokuk County Rural Health Study (1994-1998). Journal of the Academy of Audiology. 2008;19:672-685.
- Curwin B, Sanderson W, Reynolds S, Hein M, Alavanja M. Pesticide use and practices in an Iowa farm family pesticide exposure study. Journal of Agricultural Safety and Health. 2002;8(4):423-433.
- Curwin B, Hein M, Barr D, Sanderson W, Reynolds S, Ward E, Heederik D, Alavanja M. Urinary and hand wipe pesticide levels among farmers and non-farmers in Iowa. Journal of Exposure Analysis and Environmental Epidemiology. 2005;15:500-508.
- Curwin B, Hein M, Sanderson W, Nishioka M, Reynolds S, Ward E, Alavanja M. Pesticide contamination inside farm and non-farm homes. J. Occup Environ Hyg. 2005;2:357-367.
- Curwin B, Hein M, Sanderson W, Striley C, Heederik D, Kromhout H, Reynolds S, Alavanja M. Urinary pesticide concentrations among children, mothers, and fathers living in farm and non-farm households in Iowa. Annals of Occupational Hygiene. 2007;51(1):53-65.
- Curwin B. Bringing work home: Take-home pesticide exposure among farm families. Utrecht, Netherlands: Utrecht University, 2006.
- Daly JM, Stromquist AM, Jogerst GJ. Self-reported elder domestic partner violence in one rural Iowa county. Journal of Emotional Abuse. 2007;7(4):115-134.
- Ettinger RL, Warren JJ, Levy SM, Hand JS, Merchant JA, Stromquist AM. Oral health: Perceptions of need in a rural Iowa county. Journal of Special Care in Dentistry. 2004;24(1):13-21.
- Flamme, G, Mudipalli R, Reynolds S, Kelly K, Stromquist A, Zwerling C, Burmeister LF, Peng SC, Merchant J. Prevalence of hearing impairment in a rural Midwestern cohort: Estimates from the Keokuk County Rural Health Study, 1994-1998. Ear & Hearing. 2005;26(3):350-360.
- Hartz AJ, Daly JM, Kohatsu ND, Stromquist AM, Jogerst GJ, Kukoyi OA. Risk factors for insomnia in a rural population. Annals of Epidemiology. 2007;17(12):940-947.
- Humann M, Sanderson WT, Gerr F, Kelly KM, Merchant JA. Effects of common agricultural tasks on measures of hearing loss. American Journal of Industrial Medicine. 2012; 55:904-16.
- Humann M, Sanderson W, Flamme G, Kelly K, Moore G, Stromquist A, Merchant J. Noise exposures of rural adolescents. Journal of Rural Health. 2011; 27:72-80.
- Kohatsu ND, Tsai R, Young T, VanGilder R, Burmeister L, Stromquist AM, Merchant JA. Sleep duration and body mass index in a rural population. Archives of Internal Medicine. 2006;166:1701-1705.
- Lambert GP, Spurzem JR, Romberger DJ, Wyatt TA, Lyden E, Stromquist AM, Merchant JA, Von Essen SG. Tumor necrosis factor–α hyper-responsiveness to endotoxin in whole blood is associated with chronic bronchitis in farmers. Journal of Agromedicine. 2005;10(1):37-42.
- LeVan TD, Von Essen S, Lambert GP, Martinez F, Vasquez M, Merchant JA. Polymorphisms in the CD14 gene are associated with pulmonary function in farmers. American Journal of Respiratory and Critical Care Medicine. 2005;171(7):773-779.
- Merchant JA, Stromquist AM, Kelly KM, Zwerling C, Reynolds SJ, Burmeister LF. Chronic disease and injury in an agricultural county: The Keokuk County Rural Health Cohort Study. Journal of Rural Health. 2002; 18(4):521-535.
- Merchant JA, Naleway AL, Svendsen ER, Kelly KM, Burmeister LF, Stromquist AM, Taylor CD, Thorne PS, Reynolds SJ, Sanderson WT, Chrischilles EA. Asthma and farm exposures in a cohort of rural Iowa children. Environmental Health Perspectives. 2005;113(3):350-356.
- Murty SA, Peek-Asa C, Zwerling C, Stromquist AM, Burmeister LF, Merchant JA. Physical and emotional partner abuse reported by men and women in a rural community. American Journal of Public Health. 2003;93(7):1073-1075.
- Myers KP, Olsen CW, Setterquist SF, Capuano AW, Donham KJ, Thacker EL, Merchant JA, Gray GC. Are swine workers in the United States at increased risk of infection with zoonotic influenza virus? Clinical Infectious Diseases. 2006;42(1):14-20.
- Nordstrom DL, Zwerling C, Stromquist AM. Frequency, characteristics, and child and parent risk factors for nonfatal injury in rural children. Annals of Epi. 2000;10(7):452.
- Nordstrom DL, Zwerling C, Stromquist AM, Burmeister LF, Merchant JA. Rural population survey of behavioral and demographic risk factors for loaded firearms in rural households. Injury Prevention. 2001;7:112-116.
- Nordstrom DL, Zwerling C, Stromquist AM, Burmeister LF, Merchant JA. Epidemiology of unintentional adult injury in a rural population. The Journal of Trauma Injury, Infection, and Critical Care. 2001;51(4):758-766.
- Nordstrom DL, Zwerling C, Stromquist AM, Burmeister LF, Merchant JA. Identification of risk factors for non-fatal child injury in a rural area: Keokuk County Rural Health Study. Injury Prevention. 2003;9:235-240.
- Park H, Reynolds SJ, Kelly KM, Stromquist AM, Burmeister LF, Zwerling C, Merchant JA. Characterization of agricultural tasks performed by youth in the Keokuk County Rural Health Study. Applied Occupational and Environmental Hygiene. 2003;18(6):418-429.
- Pavilonis BT, Anthony TR, O’Shaughnessy PT, Humann MJ, Merchant JA, Moore G, Thorne PS, Weisel CP, Sanderson WT. Indoor and outdoor particulate matter and endotoxin concentrations in an intensely agricultural county. Journal of Exposure Science and Environmental Epidemiology. 2013; 23(3):299-305.
- Pavilonis BT, Sanderson WT, Merchant JA. Relative exposure to swine animal feeding operations and childhood asthma prevalence in an agricultural cohort. Environmental Research. 2013; 122:74-80.
- Pavilonis BT, O’Shaughnessy P, Altmaier R, Metwali N, Thorne PS. Passive monitors to measure hydrogen sulfide near concentrated animal feeding operations. Environ Sci Process Impacts. 2013 May 29; 15(6):1271-8.doi: 10. 1039/c3em00082f. PMID: 23681048.
- Peek-Asa C, Zwerling C, Young T, Stromquist A, Burmeister L, Merchant JA. A population-based study of reporting patterns and characteristics of men who abuse their female partners. Injury Prevention. 2005; 11(3):180-185.
- Peek-Asa C, Allareddy V, Yang J, Taylor C, Lundell J, Zwerling C. When one is not enough: Prevalence and characteristics of homes not adequately protected by smoke alarms. Injury Prevention. 2005;11(6):364-368.
- Peek-Asa C, Maxwell L, Stromquist A, Whitten P, Limbos A, Merchant J. Does parental physical violence reduce children’s standardized test score performance? Annals of Epidemiology. 2007;17(11):847-853.
- Renner L.M., Habib L., Stromquist A.M., Peek-Asa C. The association of intimate partner violence and depressive symptoms in a cohort of rural couples. Journal of Rural Health 2014; 30(1)50-8.
- Reynolds SJ, Merchant JA, Zwerling C, Stromquist AM, Burmeister LF. The Keokuk County Rural Health Study: Preliminary results of environmental exposure assessments. Journal of Agromedicine 1997;4:55-62.
- Reynolds SJ, Merchant JA, Stromquist AM, Burmeister LF, Taylor C, Lewis MQ, Kelly KM. The Keokuk County Rural Health Study: Self-reported use of pesticides and protective equipment. Journal of Agricultural Safety and Health, Special Issue. 1998;(1):67-77.
- Reynolds SJ, Tadevosyan A, Fuortes L, Merchant JA, Stromquist AM, Burmeister LF, Taylor C, Kelly KM. Keokuk County Rural Health Study: Self-reported use of agricultural chemicals and protective equipment. Journal of Agromedicine. 2007;12(3):45-55.
- Sanderson WT, Madsen MD, Rautiainen R, Kelly KM, Zwerling C, Taylor CD, Reynolds SJ, Stromquist AM, Burmeister LF, Merchant JA. Tractor-overturn concerns in Iowa: perspectives from the Keokuk County Rural Health Study. Journal of Agricultural Safety and Health. 2006;12(1):71-81.
- Stromquist AM, Merchant JA, Burmeister LF, Zwerling C, Reynolds SJ. The Keokuk County Rural Health Study: Methodology and demographics. Journal of Agromedicine 1997;4:243-248.
- Stromquist AM, Merchant JA, Zwerling C, Burmeister LF, Sanderson WT, Kelly KM. Challenges of conducting a large rural prospective population-based cohort study: The Keokuk County Rural Health Study. Journal of Agromedicine. 2009;14:142-149.
- Svendsen ER, Reynolds SJ, Zwerling C, Burmeister LF, Stromquist AM, Taylor CD, Merchant JA. Plotting rural households where map details are insufficient: The use of GPS in the Keokuk County Rural Health Study. Proceedings of the 3rd National GIS in Public Health Conference. San Diego, CA, ATSDR. 2000:635-638.
- Svendsen, ER, Naleway, AL, Reynolds, SJ, Taylor, CD, Thorne PS, Stromquist, AM, Merchant JA. Exposure to antibiotic feed additives and asthma in U.S. farm children. Abstract. American Journal of Respiratory and Critical Care Medicine. 2003;167(7):A155.
- Taylor CD, Reynolds SJ, Stromquist A, Merchant J, Zwerling C, Kelly K. Environmental conditions in the homes of a rural Iowa county. Journal of Agricultural Safety and Health. 1999;5(4):407-416.
- Taylor CD, Reynolds SJ. Comparison of a direct-reading device to gravimetric methods for evaluating organic dust aerosols in an enclosed swine production environment. Applied Occupational and Environmental Hygiene. 2001;16(1):78-83.
- Tiesman HM, Peek-Asa C, Whitten P, Sprince NL, Zwerling C. Depressive symptoms as a risk factor for unintentional injury: A cohort study in a rural county. Injury Prevention. 2006;12:172-177.
- Turvey C, Stromquist AM, Kelly KM, Zwerling C, Merchant JA,. Financial loss and suicidal ideation in a rural community sample. Acta Psychiatrica Scandinavica. 2002;106:373-380.
- Wright AL, Merchant JA, Stromquist AM, Kelly KM. Perinatal and early life risk factors for childhood asthma in a rural Iowa cohort. Abstract. American Journal of Epidemiology. 2000 (June suppl.)
- Yang G, O’Gara EK, Cheng G*, Kelly KM, Ramirez MR, Burmeister LF, Merchant JA. At What Age Should Children Engage in Agricultural Tasks? Journal of Rural Health. 2013; 28:372-9.
- Yang J, Peek-Asa C, Allareddy V, Zwerling C, Lundell J. Perceived risk of home fire and escape plans in rural households. American Journal of Preventive Medicine. 2006;30(1):7-12.
- Yang J, Peek-Asa C, Jones MP, Nordstrom DL, Taylor C, Young TL, Zwerling C. Smoke alarms by type and battery life in rural households: a randomized controlled trial. American Journal of Preventive Medicine. 2008;35(1):20-24.
- Zwerling C, Merchant JA, Reynolds SJ, Burmeister LF, Stromquist AM. Risk factors for injury in rural Iowa: Preliminary data from the Keokuk County Rural Health Study. Journal of Agromedicine 1997;4:295-302.
- Zwerling C, Merchant JA, Nordstrom DL, Stromquist AM, Burmeister LF, Reynolds SJ, Kelly KM. Risk factors for injury in rural Iowa: Round one of the Keokuk County Rural Health Study. American Journal of Preventive Medicine. 2001;20(3):230-233.