The frequency of acute illness in elite level athletes during international competition has been studied in a variety of settings including the Summer and Winter Olympic Games, Winter Youth Olympic Games, Summer and Winter Paralympic Games, and other international athletic and aquatic sport competitions (Table 1). These data indicate that in major international games lasting 9-18 days, 6-17% of registered athletes are likely to suffer an illness episode. Interestingly, illness appears to be consistently more common in female athletes compared with their male counterparts, which is the opposite of what is found for the general adult population. Furthermore, the incidence of illness appears to be higher in winter compared with summer Olympic Games and data from one study indicate that athletes with disability participating in the Paralympic Games appear to have a higher incidence of illness than athletes competing in the Olympic Games.
The most common illnesses are those affecting the respiratory tract with most studies indicating that about 40-60% of all acute illness episodes in athletes during competitions and tournaments affect the respiratory tract. Common symptoms of an upper respiratory illness include a sore throat, headache, fatigue, runny nose and/or watery eyes. Other parts of the body commonly affected by illness are the digestive system (10-20%), skin and underlying tissues (10-15%) and the genitourinary system (5-10%). Infections are generally reported as the most common cause of acute illness, with infection being the cause of respiratory tract illness in about 75% of cases. However, it is acknowledged that athletes can develop symptoms (e.g. sore throat, sinus congestion, cough) that mimic an infection but that the symptoms can be due to allergy or inflammation from other causes such as inhalation of cold, dry or polluted air.
Acute illness can cause a reduction in exercise performance, an interruption to training, and even result in missing an important competition. Acute infective illness can affect a number of organ systems causing a reduction in exercise performance through a number of mechanisms including: impaired motor coordination, decreased muscle strength, decreased aerobic capacity, and alterations in metabolic function. Furthermore, the presence of fever causes a decrease in the body’s ability to regulate body temperature and increases fluid losses, thereby impairing endurance performance. It has also been documented that a decrease in exercise performance after full recovery from a respiratory illness can last for 2 to 4 days and data from one study indicates that runners who start an endurance race with systemic symptoms of an acute illness are 2-3 times less likely to complete the race. It has also been reported, that in 33% of cases, an infection (most commonly of the respiratory tract) was the reason why elite Great Britain athletes from 30 different Olympic sports miss training sessions, Perhaps more importantly, an acute infective illness can also increase the risk of serious medical complications and even sudden death during strenuous exercise.
Outside of competition, the most common illnesses in athletes (and in the general population) are also viral infections of the upper respiratory tract (i.e. the common cold) which are more common in the winter months. Adults typically experience two to four episodes per year, although this can be higher during intensified training and competition due to the additional physiological and psychological stress.
There are many potential risk factors that are associated with acute illness in athletes (Figure 1). There is now some convincing evidence that an increased training load, competition load, and psychological stress together with international travel may all be risk factors for illness in the elite modern-day professional athlete. Prolonged bouts of strenuous exercise have been shown to result in transient depression of white blood cell immune functions and it is suggested that such changes create an “open window” of decreased host protection, during which viruses and bacteria can gain a foothold, increasing the risk of developing an infection (Gleeson et al. 2013). Other factors such as lack of sleep and inadequate nutrition (particularly deficiencies of protein and essential micronutrients) can also depress immunity (Gleeson 2016) and lead to increased risk of infection. There are also some situations in which an athlete’s exposure to infectious agents may be increased, which is the other important determinant of infection risk.
Gleeson M (2016) Immunological aspects of sport nutrition. Immunology and Cell Biology 94:117–123.
Gleeson M, Bishop NC and Walsh NP (2013) Exercise Immunology. London: Routledge (Taylor and Francis). ISBN 978-0-415-50725-7 (Hb); 978-0-415-50726-4 (Pb); 978-0-203-12641-7 (Ebook).