The main aim of this study was to assess the impact of travelling in high incidence tuberculosis countries on the diagnostic delays, in foreign-born persons. Results show that, among these persons, and since arrival in France, those who travelled had a quite equivalent mean diagnostic delays than those who do not travel. These results might suggest the same mechanism, a recent latent tuberculous infection that progressed to active tuberculosis. It might also suggest that, among those who did not develop TB In the first 2 years since arrival, the risk is constant throughout years. We do not find a link between travelling in high incidence countries and diagnostic delays.
The latent tuberculosis infection risk concept after travelling to high incidence tuberculous countries has been studied several times. It has been shown that travelling to such countries is a risk factor of LTBI. In a Dutch study published in 2000(6), where authors wanted to estimate the risk of infection after travelling to high incidence countries, in non-vaccinated BCG persons with a negative tuberculin skin test (TST), a 1,8% rate of LTBI was noted 2 to 4 months after their return, and 0,3% were diagnosed active tuberculosis. Working in a health facility in these countries was associated with an increased risk of LTBI (RR = 5.34; p = 0.015). In an American study(7) where authors estimated the influence on results of TSTs in children, in the last 12 months following a travel in high incidence countries, 7.6% of these children had a positive TST. The risk of positivity was significantly associated with an history of travelling in the last 12 months (RR = 3,9; 95% CI 1.9–7.9). Countries or regions where these children travelled were Mexico, Central America and South East Asia. Children in contact with persons from high incidence countries had an increased risk of a positive TST (OR = 2.4; 95% CI 1-5.5).
This risk is also concerning active TB. A 1984 British study(8) already noted that 20% of tuberculosis cases in Asian immigrants was associated with a travel back to their birth countries. As well, a Dutch study(9), who wanted to see, among persons born in Morocco or Turkey who travelled to their birth country in the last 12 months, but in the Netherlands for less than 2 years, the risk of diagnosing tuberculosis was 3.2 times higher than persons who did not travel (95% CI 1.3–7.7). Among Turkish patients, history of travelling was a not a significant risk factor (OR = 0.9; 95% CI 0.3–2.4). A greater incidence of tuberculosis in Morocco than in Turkey was the main explanation of the authors (which, in 2006, was 97/100 000 in Morocco versus 33/100 000 in Turkey, according to the World Bank data). The risk was even higher if the person had a long journey in this country, with a 17 times risk of developing TB if the length of stay was more than 3 years.
The statement was even more striking when distinction was made between tourists and travelers native to these countries. In a British study(10), among 1032 tuberculous patients from India declared to the health authorities between 1978 and 1997, 22% had an history of travel and 66% of them in the last 3 years preceding the diagnosis.
Our results are in line with these previous studies, mentioning the increased risk of tuberculosis following a travel in high incidence countries.
These results also raise questions about the quite similar diagnosis delays. The similarity of the distribution of data in Figs. 4 and 5 suggest that immigrants coming from high incidence countries develop tuberculosis either before the migration (early tuberculosis) or either during their journey (delayed tuberculosis). Most cases occurring in the first 2 years following their arrival in France or following a trip in a high incidence country goes clearly in that direction. Travelling to such countries should be regarded as a “reset” in the risk of tuberculosis. Unexpectedly, we did not find any relation between diagnostic delays and the TB incidence of countries, as it would have been interesting to imagine that, the higher the incidence of TB is, the higher is the risk of acquiring LTBI or active TB, and the shorter the delay could have been. In fact, it seems that a documented contact with an active TB person is a better hint for predicting the delay. Difference of delays between foreign born persons and native persons who travelled to high incidence countries might be explained by a different behavior during the journey(11). It has been shown that tourists born in these countries has a greater risk of acquiring travel related infections, including tuberculosis. It could be explained by a less cautious behavior, by more frequent contact with locals. As well, the journey is often longer.
Immigrants who plan to travel to birth countries should be, therefore, aware of risks of LTBI and active TB, especially if they have susceptibility factors. A case by case screening, depending on the person and the country they visited, should be implemented. Our results support recent guidelines from French Public Health authorities, considering travels to high incidence countries in the indication for screening of LTBI among certain populations (susceptible persons, healthcare persons, expatriate in a high incidence country more than 6 months)(12).
This study has several limits. It did not allow us to develop certain linking of variables. However, as we consider the studied questions, most of records were complete. Some non-significant results could be explained by a lack of power, because of a low number of patients, and it might be relevant to repeat this study with a greater number. Finally, it could have been interessant to include the length of journey into the risk, which might have an influence.