Heat Illness Among High School Athletes --- United States, 2005--2009

Heat Illness Among High School Athletes --- United States, 2005--2009
Weekly
August 20, 2010 / 59(32);1009-1013


Heat illness during practice or competition is a leading cause of death and disability among U.S. high school athletes (1). An estimated 7.5 million students participate in high school sports annually (2). To examine the incidence and characteristics of heat illness among high school athletes, CDC analyzed data from the National High School Sports-Related Injury Surveillance Study for the period 2005--2009, which includes the 2005--06, 2006--07, 2007--08 and 2008--09 school years. During 2005--2009, the 100 schools sampled reported a total of 118 heat illnesses among high school athletes resulting in ≥1 days of time lost from athletic activity (i.e., time-loss heat illness), a rate of 1.6 per 100,000 athlete-exposures and an average of 29.5 time-loss heat illnesses per school year. The average corresponds to a weighted average annual estimate of 9,237 illnesses nationwide. The highest rate of time-loss heat illness was among football players, 4.5 per 100,000 athlete-exposures, a rate 10 times higher than the average rate (0.4) for the eight other sports. Time-loss heat illnesses occurred most frequently during August (66.3%) and while practicing or playing football (70.7%). No deaths were reported. Consistent with guidelines from the National Athletic Trainers' Association (NATA) (3), to reduce the risk for heat illness, high school athletic programs should implement heat-acclimatization guidelines (e.g., set limits on summer practice duration and intensity). All athletes, coaches, athletic trainers, and parents/guardians should be aware of the risk factors for heat illness, follow recommended strategies, and be prepared to respond quickly to symptoms of illness. Coaches also should continue to stress to their athletes the importance of maintaining proper hydration before, during, and after sports activities.

The High School Sports-Related Injury Surveillance Study (4), conducted by the Center for Injury Research and Policy at Nationwide Children's Hospital in Columbus, Ohio, has been described in detail previously (5). Each summer, study staff members e-mail all NATA-affiliated certified athletic trainers who have an e-mail address on file with NATA and invite their school to participate in the study. During 2005--2009 the number of certified athletic trainers receiving e-mails was as follows: (2005--06) 4,120; (2006--07) 3,378; (2007--08) 3,755; and (2008--09) 4,496. NATA-affiliated certified athletic trainers, who are trained in illness and injury prevention, assessment, and care, provide services to approximately 42% of the 18,753 public and private high schools in the United States (NATA, unpublished data, 2010). Following the e-mail invitation, interested schools that return a permission form signed by the principal, athletic director, and one certified athletic trainer are categorized into eight strata based on school enrollment (≤1,000 students or >1,000) and U.S. Census geographic location. Subsequently, 12 or 13 schools are chosen randomly from each of the eight strata to constitute a 100-school sample.

During the school year, study staff members e-mail participating certified athletic trainers weekly to remind them to enter their school's injury and exposure data into an online surveillance system. Data are collected on nine sports: football, wrestling, soccer, baseball, and basketball (for boys); and volleyball, soccer, basketball, and softball (for girls). For each illness or injury, the certified athletic trainer is asked to submit a detailed illness/injury report that collects data including the athlete's age, height and weight; illness setting (practice or competition); diagnosis as reported by athletic trainer; number of hours illness occurred after practice began*; and amount of time lost from athletic activity. Data such as height and weight often are measured by the certified athletic trainer but occasionally are self-reported by the athlete. Detailed exposure data, such as ambient temperature, relative humidity, or specific type of heat illness (e.g., heat cramps or heat exhaustion) are not collected. Certified athletic trainers with missing or incomplete reports are e-mailed monthly by study staff members and asked to update information; those not responding to e-mail requests are telephoned and assessed for their willingness to continue participation. During 2005--2009, 90% of the schools reported during all study weeks. Recent internal validity checks in a convenience sample of eight participating schools yielded 100% sensitivity and 99.6% specificity during the reported weeks.

Time-loss heat illness was defined as dehydration or heat exhaustion/heat stroke that 1) resulted from participation in a school-sanctioned practice or competition, 2) was assessed by a medical professional (with or without treatment), and 3) resulted in ≥1 days of time loss from athletic activity. If an athlete sustained a heat illness and returned or was cleared to return to practice or competition the next day, the heat illness was not reportable. Exposures to sports activities were measured by "athlete-exposures." One athlete-exposure was defined as one athlete participating in one practice or one competition. Rates per 100,000 athlete exposures were calculated based on the actual number of time-loss heat illnesses reported by the schools.

Each case of time-loss heat illness was assigned a sample weight on the basis of the inverse of the school selection probability, using stratifications based on school enrollment and U.S. Census geographic location. These weights were summed to provide national estimates of time-loss heat illness, from which average annual estimates were calculated. Confidence intervals were calculated by use of a direct variance estimation procedure that accounted for the sample weights and the complex sample design. Finally, although heat illness might have a geographic distribution, this study was designed to provide national estimates only.

During 2005--2009, a total of 118 time-loss heat illnesses (an average of 29.5 per school year) were reported by the 100 participating schools in the nine sports studied. These data correspond to an estimated average annual number of 9,237 (95% confidence interval [CI] = 8,357--10,116) time-loss heat illnesses nationwide. The majority of time-loss heat illnesses occurred among high school football players (70.7%), who sustained an estimated average annual 6,529 (CI = 5,794--7,264) time-loss heat illnesses. Time-loss heat illness among high school athletes occurred most frequently in August (66.3%) (Figure), the month when most schools begin preseason sports training.

The highest rate of time-loss heat illness was among football players, 4.5 per 100,000 athlete-exposures (Table 1), a rate 10 times higher than the average rate (0.4) for the eight other sports. Football time-loss heat illness rates were similar in practice (4.4) and competition (4.7) (Table 1); 76.7% occurred during preseason (Table 2). Although football practice and competition had similar rates, because more time (including preseason) is spent practicing, 83.6% of all football time-loss heat illnesses occurred during practice. Football time-loss heat illnesses during practice usually occurred 1--2 hours (46.6%) or >2 hours (37.2%) after practice had begun. The majority of illnesses (58.2%) occurred among varsity football players and among juniors (35.6%) or seniors (28.3%). Affected football players commonly had a body mass index† categorized as overweight (37.1%) or obese (27.6%). The majority of football players (63.1%) returned to play 1--2 days after illness onset.

Reported by
J Gilchrist, MD, Div of Unintentional Injury Prevention; T Haileyesus, MS, Office of Statistics and Programming, National Center for Injury Prevention and Control; M Murphy, PhD, Health Studies Br, National Center for Environmental Health, CDC. RD Comstock, PhD, Center for Injury Research and Policy, Nationwide Children's Hospital and Ohio State Univ; C Collins, MA, N McIlvain, Center for Injury Research and Policy, Nationwide Children's Hospital, Columbus, Ohio. E Yard, PhD, EIS Officer, CDC.

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Heat Illness Among High School Athletes --- United States, 2005--2009