International Travel and Increased Illness Risk in Athletes
In this study, the effects of international travel across multiple time zones (in both an easterly and westerly direction), on the incidence of illness in elite rugby players participating in the 2010 Super 14 Rugby Union tournament was documented. The main findings of this study are as follows: (1) international travel to a foreign location greater than 5 h time zone difference from the home country was associated with a significant increase (2–3 times) in the incidence of all illness, respiratory tract illness, GIT illness and all infective illness, (2) the incidence of illness was not affected by the direction of international travel (easterly or westerly direction), (3) travelling back to the home country was not associated with a increased incidence of illness compared with baseline (before travelling) and (4) the weekly incidence of illness was similar over the 4 weeks following international travel to a destination >5 time zones difference, or return international travel back to the home country.
This study, to our knowledge, is the first prospective cohort study to determine the effect of international travel on the incidence of illness in elite athletes participating in a prolonged tournament. Apart from the prolonged duration (16 weeks), intense weekly training sessions (2–3 per week) and weekly matches, the Super Rugby Union tournament is also characterised by periods where teams travel between South Africa, New Zealand and Australia (with time zone differences that vary between 2 and 11 h) to compete. We have previously shown that there is a high overall incidence of illness during this competition, mostly affecting the respiratory and the GIT systems. Infections accounted for most illnesses.
There are no published studies in travelling athletes, and indeed few prospective studies in the travel medicine literature for comparison. In one study, the illness rate (per 100 person-weeks) was reported for adults and children travelling from Europe to subtropical and tropical regions and then returning home. On the assumption that a 100 person-weeks is equivalent to 700 person-days, the incidence of all illness reported in this study during travel (33.9/100 person-weeks) can be expressed as 48.4/1000 person-days. Similarly, the incidence of illness in the 4-week period following return home was 5.7/100 person-weeks and can be expressed as 8.14/1000 person-days. It is of interest to note that these data are quite similar to our reported incidence of 32.6/1000 player-days during travel, and 10.6/1000 players days on return. However, this comparison should be made with caution as the definition and classification of illness, populations studied, time zone documentation, nature of travel and physiological systems were different between studies. Thus, the paucity of data in this area is clear, and more research is needed to determine the precise incidence of illness in travelling athletes from other sporting codes, other tournaments, different travel durations, travel destinations and travel direction (eg, north–south compared with east–west).
In our study we did not find a difference in the incidence of illness across the months of the study, with the exception of a marginal decrease in the incidence of illness during the month of April. Furthermore, there was no significant difference in the incidence of illness in teams travelling to a foreign destination in an easterly or westerly direction across multiple time zones (>5 time zones). However, the principal finding of this study was that any travel >5 time zones away from the home country was associated with a 2–3-fold increase in the incidence of all illness, respiratory illness, GIT illness and all infections. If factors during air travel (including drying of respiratory epithelium, close contact with fellow air travellers, and exposure to re-circulated air) predispose to illness, we would have also expected a high incidence of respiratory illness following return travel to the home country.
Indeed, as the incidence of illness following arrival back at home was similar to that of baseline, the results from our study indicate that the illness risk is not directly related to the travel itself, but rather the arrival and location of the team at a distant destination. We can thus conclude that various factors associated with the distant destination, rather than travel per se, are associated with the increased incidence of illness. These factors were not investigated in our study. However, it could be speculated that various possible stressors including environmental conditions (temperature, humidity, climate, altitude, pollution, and pollens), food and exposure to different cultures, populations and pathogens could all play a role. Further studies are needed to determine the role of these factors.
Finally, there is also a possibility that access to the team physician was more likely during travel and therefore it is easier to document illness. However, most teams are also accommodated and travel together during the periods when they are located at home. During these times, it is also a requirement that all illness is reported to the team physician, as they are responsible for the health of the players. Therefore, under-reporting of illness during the baseline and return periods is very unlikely.
In an attempt to investigate if there are any 'high-risk' periods of illness following travel (abroad and returning home), we also determined the incidence of illness at weekly intervals (weekly for 2 weeks) and in a 2–4-week period following travel. These results show that there is no increased risk of illness in the first compared with the 2nd to the 4th week after travel (abroad or returning home). The incidence of infective illness was however higher in the 2–4-week period during baseline. The reasons for this are not clear, but may be related to the transmissions of pathogens are possible when players that get together for the first time in the season. Many pathogens have an incubation period that would result in manifestations of illness after 7 days. This finding needs to be confirmed but team physicians can take note of this higher risk period at the onset of the tournament and institute measures to reduce the risk of illness.
The strengths of the present study are that it represents the largest prospective cohort study on the effects of international travel on the incidence of illness in elite athletes. Furthermore, team physicians accurately reported the incidence of clearly defined illness on a daily basis, with a very high compliance rate.
The main limitations of this study are that the results cannot necessarily be applied to other sporting codes and tournaments, to the recreational or business traveller, or to long-distance travel that does not cross multiple time zones such as north–south travel. Furthermore, we cannot account for any possible confounders such as possible illness prevention measures that team physicians employed in their teams.
The clinical relevance of the findings from this study is important to team physicians. While we have previously documented that players generally present to the team physician with illness 24 h or more after the onset of symptoms, the data from the current study allow the team physician to identify a period before and during travel where athletes are at higher risk and can allow for increased vigilance.
Although specific risk factors associated with the increased incidence of illness during travel away from home require further research, team physicians can adopt certain strategies to reduce the risk of illness based on (1) some known risk factors from studies in the travel medicine literature and (2) an one report of successful reduction in illness in athletes. General risk factors for illness during travel in non-athletes are age (increased risk in the third decade), female sex, inexperienced travellers, summer season and large climatic contrast from the home country. However, further studies should be planned to determine risk factors (intrinsic and extrinsic) for illness in athletes following travel to international destinations.
In summary, the modern-day elite athlete is increasingly required to travel across multiple time zones in order to participate in international tournaments. The team physician is responsible for protection of the health of the athlete during these periods of travel and competition. This study shows for the first time that elite athletes travelling to international destinations >5 time zone differences from their home country is associated with a 2–3 times increased risk of all illness, respiratory tract illness, GIT illness and all infective illness. Identification of this period where athletes are at higher risk allows the team physician to plan certain preventative measures and have increased vigilance during this time.
Discussion
In this study, the effects of international travel across multiple time zones (in both an easterly and westerly direction), on the incidence of illness in elite rugby players participating in the 2010 Super 14 Rugby Union tournament was documented. The main findings of this study are as follows: (1) international travel to a foreign location greater than 5 h time zone difference from the home country was associated with a significant increase (2–3 times) in the incidence of all illness, respiratory tract illness, GIT illness and all infective illness, (2) the incidence of illness was not affected by the direction of international travel (easterly or westerly direction), (3) travelling back to the home country was not associated with a increased incidence of illness compared with baseline (before travelling) and (4) the weekly incidence of illness was similar over the 4 weeks following international travel to a destination >5 time zones difference, or return international travel back to the home country.
This study, to our knowledge, is the first prospective cohort study to determine the effect of international travel on the incidence of illness in elite athletes participating in a prolonged tournament. Apart from the prolonged duration (16 weeks), intense weekly training sessions (2–3 per week) and weekly matches, the Super Rugby Union tournament is also characterised by periods where teams travel between South Africa, New Zealand and Australia (with time zone differences that vary between 2 and 11 h) to compete. We have previously shown that there is a high overall incidence of illness during this competition, mostly affecting the respiratory and the GIT systems. Infections accounted for most illnesses.
There are no published studies in travelling athletes, and indeed few prospective studies in the travel medicine literature for comparison. In one study, the illness rate (per 100 person-weeks) was reported for adults and children travelling from Europe to subtropical and tropical regions and then returning home. On the assumption that a 100 person-weeks is equivalent to 700 person-days, the incidence of all illness reported in this study during travel (33.9/100 person-weeks) can be expressed as 48.4/1000 person-days. Similarly, the incidence of illness in the 4-week period following return home was 5.7/100 person-weeks and can be expressed as 8.14/1000 person-days. It is of interest to note that these data are quite similar to our reported incidence of 32.6/1000 player-days during travel, and 10.6/1000 players days on return. However, this comparison should be made with caution as the definition and classification of illness, populations studied, time zone documentation, nature of travel and physiological systems were different between studies. Thus, the paucity of data in this area is clear, and more research is needed to determine the precise incidence of illness in travelling athletes from other sporting codes, other tournaments, different travel durations, travel destinations and travel direction (eg, north–south compared with east–west).
In our study we did not find a difference in the incidence of illness across the months of the study, with the exception of a marginal decrease in the incidence of illness during the month of April. Furthermore, there was no significant difference in the incidence of illness in teams travelling to a foreign destination in an easterly or westerly direction across multiple time zones (>5 time zones). However, the principal finding of this study was that any travel >5 time zones away from the home country was associated with a 2–3-fold increase in the incidence of all illness, respiratory illness, GIT illness and all infections. If factors during air travel (including drying of respiratory epithelium, close contact with fellow air travellers, and exposure to re-circulated air) predispose to illness, we would have also expected a high incidence of respiratory illness following return travel to the home country.
Indeed, as the incidence of illness following arrival back at home was similar to that of baseline, the results from our study indicate that the illness risk is not directly related to the travel itself, but rather the arrival and location of the team at a distant destination. We can thus conclude that various factors associated with the distant destination, rather than travel per se, are associated with the increased incidence of illness. These factors were not investigated in our study. However, it could be speculated that various possible stressors including environmental conditions (temperature, humidity, climate, altitude, pollution, and pollens), food and exposure to different cultures, populations and pathogens could all play a role. Further studies are needed to determine the role of these factors.
Finally, there is also a possibility that access to the team physician was more likely during travel and therefore it is easier to document illness. However, most teams are also accommodated and travel together during the periods when they are located at home. During these times, it is also a requirement that all illness is reported to the team physician, as they are responsible for the health of the players. Therefore, under-reporting of illness during the baseline and return periods is very unlikely.
In an attempt to investigate if there are any 'high-risk' periods of illness following travel (abroad and returning home), we also determined the incidence of illness at weekly intervals (weekly for 2 weeks) and in a 2–4-week period following travel. These results show that there is no increased risk of illness in the first compared with the 2nd to the 4th week after travel (abroad or returning home). The incidence of infective illness was however higher in the 2–4-week period during baseline. The reasons for this are not clear, but may be related to the transmissions of pathogens are possible when players that get together for the first time in the season. Many pathogens have an incubation period that would result in manifestations of illness after 7 days. This finding needs to be confirmed but team physicians can take note of this higher risk period at the onset of the tournament and institute measures to reduce the risk of illness.
The strengths of the present study are that it represents the largest prospective cohort study on the effects of international travel on the incidence of illness in elite athletes. Furthermore, team physicians accurately reported the incidence of clearly defined illness on a daily basis, with a very high compliance rate.
The main limitations of this study are that the results cannot necessarily be applied to other sporting codes and tournaments, to the recreational or business traveller, or to long-distance travel that does not cross multiple time zones such as north–south travel. Furthermore, we cannot account for any possible confounders such as possible illness prevention measures that team physicians employed in their teams.
The clinical relevance of the findings from this study is important to team physicians. While we have previously documented that players generally present to the team physician with illness 24 h or more after the onset of symptoms, the data from the current study allow the team physician to identify a period before and during travel where athletes are at higher risk and can allow for increased vigilance.
Although specific risk factors associated with the increased incidence of illness during travel away from home require further research, team physicians can adopt certain strategies to reduce the risk of illness based on (1) some known risk factors from studies in the travel medicine literature and (2) an one report of successful reduction in illness in athletes. General risk factors for illness during travel in non-athletes are age (increased risk in the third decade), female sex, inexperienced travellers, summer season and large climatic contrast from the home country. However, further studies should be planned to determine risk factors (intrinsic and extrinsic) for illness in athletes following travel to international destinations.
In summary, the modern-day elite athlete is increasingly required to travel across multiple time zones in order to participate in international tournaments. The team physician is responsible for protection of the health of the athlete during these periods of travel and competition. This study shows for the first time that elite athletes travelling to international destinations >5 time zone differences from their home country is associated with a 2–3 times increased risk of all illness, respiratory tract illness, GIT illness and all infective illness. Identification of this period where athletes are at higher risk allows the team physician to plan certain preventative measures and have increased vigilance during this time.
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