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Journal of Safety Research 41 (2010) 471–474
Special Report from the CDC
Heat illness among high school athletes —United States, 2005–2009
Ellen E. Yard
a,
⁎, Julie Gilchrist
b
, Tadesse Haileyesus
c
, Matthew Murphy
a
, Christy Collins
d
,
Natalie McIlvain
d
, R. Dawn Comstock
d,e
a
Health Studies Branch, Division of Environmental Hazards and Health Effects, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA, United States
b
Division of Unintentional Injury Prevention, National Center for Injury Prevention and Control, Centers for Disease Control and Prevention, Atlanta, GA, United States
c
Office of Statistics and Programming, National Center for Injury Prevention and Control, Centers for Disease Control and Prevention, Atlanta, GA, United States
d
Center for Injury Research and Policy, The Research Institute at Nationwide Children's Hospital, Columbus, OH, United States
e
College of Medicine, Department of Pediatrics and College of Public Health, Division of Epidemiology, The Ohio State University, Columbus, OH, United States
The Journal of Safety Research has partnered with the Office of the Associate Director for Science, Division of Unintentional Injury Prevention at the Centers for Disease Control and
Prevention (CDC) in Atlanta, Georgia, USA, to briefly report on some of the latest findings in the research community. This report is the 20
th
in a series of CDC articles.
abstractarticle info
Article history:
Received 28 September 2010
Accepted 28 September 2010
Available online 13 October 2010
Keywords:
Heat illness
Sports
Adolescents
Unintentional injury
Climate change
Introduction: Heat illness is a leading cause of death and disability among U.S. high school athletes. Methods:
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. Results:
During 2005–2009, the 100 schools sampled reported a total of 118 heat illnesses among high school athletes
resulting in ≥1 day of time lost from athletic activity, 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. Conclusions: Consistent with guidelines from the National
Athletic Trainers’Association, 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 sportsactivities. Impactof industry: By implementing preventive recommendations and quickly recognizing
and responding to heat illness, coaches, athletic trainers, and the sporting community can prevent future deaths.
National Safety Council and Elsevier Ltd. All rights reserved.
1. Introduction
Heat illness encompasses a spectrum of illness that includes muscle cramps, heat syncope, heat exhaustion, exertional heat stroke, and exertional
hyponatremia (Binkley, Beckett, Casa, Kleiner, & Plummer, 2002). Symptoms can be both physical (e.g., dehydration, thirst, fatigue, dizziness,
lightheadedness, weakness) as well as neurological (e.g., confusion, disorientation, loss of consciousness; Binkley et al.). Although heat illness is
preventable, it is the leadingcause of death and disabilityamong U.S. high school athletes (Mueller & Cantu, 2008). In 2010, anestimated7.5 million
studentsparticipated in high school sports annually (National Federation of St ate High School Associations, 2010). Despite thehigh incidence andthe
large population at risk, no study has yet to investigate heat illness incidence among a nationally representative sample of U.S. high school athletes.
2. Methods
The High School Sports-Related Injury Surveillance Study (CDC, 2006), conducted by the Center for Injury Research and Policy at Nationwide
Children's Hospital, has been described in detail previously (Collins, McIlvain, Yard, & Comstock, 2009). Briefly, all high schools with ≥1 National
Abbreviations: NATA, National Athletic Trainers’Association; CI, Confidence Interval; CDC, Centers for Disease Control and Prevention.
⁎Corresponding author. CDC/NCEH/Health Studies Branch, 4770 Buford Hwy, MS F-57, Chamblee, GA 30341, United States. Tel.: +1 770 488 3406; fax: +1 770 488 3450.
E-mail address: eyard@cdc.gov (E.E. Yard).
0022-4375/$ –see front matter. National Safety Council and Elsevier Ltd. All rights reserved.
doi:10.1016/j.jsr.2010.09.001
Contents lists available at ScienceDirect
Journal of Safety Research
journal homepage: www.elsevier.com/locate/jsr
Author's personal copy
1
Body mass index (BMI) =weight (kg) / [height (m
2
)]. BMI classifications: b18.5 underweight, 18.5–24.9 normal weight, 25–29.9 overweight, ≥30 obese.
2
http://www.unc.edu/depts/nccsi/2009AnnualFootball.pdf.
Athletic Trainers’Association (NATA)–affiliated certified athletic trainer (ATCs) with a valid e-mail address are invited to participate. Willing
participants are categorized into eight strata based on school population (enrollment ≤1000 or N1000) and U.S. Census geographic location
(Northeast, Midwest, South, and West). From these eight strata, 100 high schools are randomly chosen to participate. During the school year,
participating ATCs enter their school's injury and exposure data weekly 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).
Time-loss heat illness was defined as dehydration or heat exhaustion/heat stroke that: (a) resulted from participation in a school-sanctioned
practice or competition; (b) was assessed by a medical professional; and (c) resulted in ≥1 day 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. 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.
3. Results
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%; Fig. 1), 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. 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 N2 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
1
categorized as overweight (37.1%) or
obese (27.6%). Although the majority of football players (63.1%) returned to play 1–2 days after illness onset, 18.4% missed 3-6 days, 9.7% missed
7-21 days, and 3.0% discontinued their season.
4. Discussion
This analysis is the first to report national estimates for time-loss heat illness among high school athletes. The findings in this report indicate
that time-loss heat illness occurred most frequently among football players (4.5 time-loss heat illnesses per 100,000 athlete-exposures) and
during August (66.3%) and are consistent with previous studies reporting that football players accounted for 5.3% of all nonfatal heat-related
visits to emergency departments (Sanchez, Thomas, Malilay, & Annest, 2010) and that 88% of football heat illnesses occurred in August (Cooper,
Ferrara, & Broglio, 2006). This study found that 64.7% of football players sustaining a heat illness were either overweight or obese. Obesity has
been shown to be a risk factor for heat illness because fat decreases heat loss; a previous study reported that 47.1% of all high school football
players were overweight or obese (Choate, Forster, Almquist, Olsen, & Poth, 2007). In the absence of prompt intervention, heat illness can result
in permanent morbidity (e.g., neurologic, cardiac, renal, gastrointestinal, hematologic, or muscle dysfunction) or mortality. These results support
the existing NATA recommendations to continue emphasis of appropriate primary and secondary prevention strategies.
All heat illnesses in high school athletes are preventable. Since 1995, according to an annual survey of catastrophic football injuries, 31 high
school football players have died from heat stroke.
2
One component of primary prevention is the implementation of acclimatization periods to
Fig. 1. Number (n = 101
a
) of time-loss heatillnesses
b
among high schoolathletes, by month—National High School Sports-Related Injury Surveillance Study,
c
United States, 2005–2009.
a
Excludes 17 cases with missing dates.
b
Defined as 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.
c
Data based on reports from a 100-school sample.
472 E.E. Yard et al. / Journal of Safety Research 41 (2010) 471–474
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prepare participants for strenuous activity in warm or humid weather. Acclimatization is particularly important during preseason football
practices, which typically occur during the hottest and most humid period of summer and when participants are least physically fit. Current NATA
recommendations suggest implementation of a 14-day acclimatization period for all warm weather conditioning, with practice frequency,
duration, and intensity as well as protective equipment usage increased gradually (Binkley et al., 2002; Casa & Csillan, 2009). Another primary
prevention strategy is educating participants regarding the signs and symptoms of heat-related illness and the importance of proper hydration
before, during, and after strenuous activity (Binkley et al., 2002). Fluid replacement should approximate sweat and urine losses so that athletes
lose no more than 2% body weight per day. According to NATA, on average, this equates to consuming 200–300 mL fluid every 10–20 minutes
during exercise (Casa et al., 2000).
Ambient temperature, relative humidity, wind speed, and solar radiant heat all affect risk for heat illness (Binkley et al., 2002). For example,
although NATA guidelines suggest that a temperature of 90 degrees at 20% humidity could be suitable for conducting football practice with full
protective gear, a temperature of 90 degrees at 80% humidity could create a dangerousenvironment for which activity and equipment use should
be limited (Binkley et al., 2002). Thus, NATA recommends that coaches and athletic administrators monitor ambient temperature and relative
humidity and be prepared to implement appropriate activity restrictions (Binkley et al., 2002).
Once a participant shows signs of heat illness, secondary prevention is crucial to prevent progression. Any person exhibiting nausea, vomiting,
headache, dizziness, or mental status change should be immediately evaluated for potential heat exhaustion or heat stroke by a health
professional (Binkley et al., 2002). In mild cases of heat illness (i.e., dehydration or heat cramps), simple interventions that include removal from
activity and rehydration can be sufficient. However, more advanced conditions, such as heat exhaustion or heat stroke, require aggressive
interventions such as cold water immersion and chilled intravenous fluids to lower core body temperature as rapidly as possible (Binkley et al.,
2002; Casa et al., 2000).
The findings in this report are subject to at least one limitation. These results are an underestimate of the actual magnitude of heat illness
among high school athletes because only heat illnesses resulting in ≥1 days time loss were reportable, only nine sports were assessed, and only
schools with an NATA-affiliated certified athletic trainer were included.
If left untreated, heat illness can progress to heat stroke and result in permanent illness or death; thus, prevention is critical. Athletes, coaches,
athletic trainers, and parents/guardians should be aware of the hazards and risk factors, follow recommended prevention strategies, and be
prepared to respond quickly. CDC is developing an Internet-based course for coaches and others associated with high school athletics to help
prevent, recognize, and respond to heat-related illness among student athletes.
References
Binkley, H. M., Beckett, J., Casa, D. J., Kleiner, D. M., & Plummer, P. E. (2002). National Athletic Trainers’Association position statement: exertional heat illnesses. Journal of Athletic
Training,37, 329−343.
Casa, D. J., Armstrong, L. E., Hillman, S. K., Montain, S. J., Reiff, R. V., Rich, B. S. E., et al. (2000). National Athletic Trainers’Association Position Statement: Fluid Replacement for
Athletes. Journal of Athletic Training,35, 212−224.
Casa, D. J., & Csillan, D. (2009). Preseason heat-acclimatization guidelines for secondary school athletics. Journal of Athletic Training,44, 332−333.
Centers for Disease Control and Prevention [CDC]. (2006). Sports-related injuries among high school athletes—United States, 2005–06 school year. MMWR,55, 1037−1040.
Choate, N., Forster, C., Almquist, J., Olsen, C., & Poth, M. (2007). The prevalence of overweight in participants in high school extramural sports. The Journal of Adolescent Health,40,
283−285.
Collins, C.L., McIlvain, N.M., Yard, E.E., & Comstock, R.D. (2009). National High School Sports-Related Injury Surveillance Study—2008–09 school year. Columbus, OH: Nationwide
Children's Hospital. Available at http://injuryresearch.net/resources/1/rio/2008-09highschool%20riosummaryreport.pdf. Accessed August 13, 2010.
Cooper, E. R., Ferrara, M. S., & Broglio, S. P. (2006). Exertional heat illness and environmental conditions during a single football season in the southeast. Journal of Athletic Training,41,
332−336.
Mueller, F.O. & Cantu, R.C. (2008). Catastrophic sports injury research: twenty-sixth annual report. Chapel Hill, NC: University of North Carolina. Available at http://www.unc.edu/
depts/nccsi/AllSport.pdf. Accessed August 13, 2010.
National Federation of State High School Associations. (2010). Participation survey results. Indianapolis, IN: National Federation of State High School Associations. Available at http://
www.nfhs.org/participation. Accessed August 13, 2010.
Sanchez, C. A., Thomas, K. E., Malilay, J., & Annest, J. L. (2010). Nonfatal natural and environmental injuries treated in emergency departments, United States, 2001–2004. Family &
Community Health,33,3−10.
Table 1
Number (n =118) and rate
a
of time-loss heat illnesses
b
among high school athletes, by sport and practice or competition setting—National High School Sports-Related Injury
Surveillance Study,
c
United States, 2005–2009.
Sport Practice Competition Overall
n Rate n Rate n Rate
Overall 88 1.7 30 1.6 118 1.6
Boys’sports 83 2.1 22 1.7 105 2.0
Football 77 4.4 17 4.7 94 4.5
Wrestling 2 0.4 3 1.7 5 0.7
Soccer 0 - 2 0.9 2 0.3
Baseball 2 0.4 0 - 2 0.3
Basketball 2 0.3 0 - 2 0.2
Girls’sports 5 0.4 8 1.3 13 0.6
Volleyball 5 1.2 1 0.5 6 0.9
Soccer 0 - 5 2.5 5 0.8
Basketball 0 - 2 0.9 2 0.3
Softball 0 - 0 - 0 -
a
Per 100,000 athlete-exposures (i.e., practice or competition).
b
Defined as 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.
c
Data based on reports from a 100-school sample.
473E.E. Yard et al. / Journal of Safety Research 41 (2010) 471–474
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Ellen E. Yard,PhD, is an Epidemic Intelligence Service Officer assigned to the National Center for Environmental Health at CDC. Her work focuses on environmental and injury
epidemiology.
Julie Gilchrist,MD, is a pediatrician and medical epidemiologist with the National Center for Injury Prevention and Control at the CDC. She is responsible for research and programs
in sports and recreation-related injury prevention, drowning prevention, and dog bite prevention.
Tadesse Haileyesusi,MS, is a mathematical statistician working in the Office of Statistics and Programming, National Center for Injury Prevention and Control at the CDC. He is a
lead statistician for the National Electronic Injury Surveillance System-All Injury Program data quality assurance, and provides statistical programming and analyses.
Matthew Murphy,PhD, is an epidemiologist at the National Center for Environmental Health at the CDC. He is responsible for investigating a variety of environmental health
issues, including heat and cold illnesses, safe water issues in vulnerable populations, chemical exposures, and illness outbreaks.
Christy Collins,MA, is a Senior Research Associate in the Center for Injury Research and Policy of The Research Institute at Nationwide Children's Hospital. She is responsible for the
coordination and daily maintenance of the National High School Sports-Related Injury Surveillance Study.
Natalie McIlvain,BS, is a Research Assistant in the Center for Injury Research and Policy of The Research Institute at Nationwide Children's Hospital. She is responsible for the data
analysis and preparation of study-related reports for the National High School Sports-Related Injury Surveillance Study.
R Dawn Comstock,PhD, is on the research faculty at the Center for Injury Research and Policy of The Research Institute at Nationwide Children’s Hospital. Her main interests are
the epidemiology of sports, recreation and leisure activity-related injuries among children and adolescents as well as the life-long health benefits associated with an active
childhood.
474 E.E. Yard et al. / Journal of Safety Research 41 (2010) 471–474
