Tuberculosis is an airborne infection. Droplet nuclei produced by a source individual with active pu

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The Committee to Advise on Tropical Medicine and Travel (CATMAT) provides the Public Health Agency of Canada (PHAC) with ongoing and timely medical, scientific, and public-health advice relating to tropical infectious disease and health risks associated nile cruise ship reviews with international travel. PHAC acknowledges that the advice and recommendations set out in this statement are based upon the best current available scientific knowledge and medical practices, and is disseminating this document for information purposes to both travellers and the medical community caring for travellers.
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One third of the world's population is infected with Mycobacterium tuberculosis . Over nine million people developed active nile cruise ship reviews tuberculosis (TB) in 2007, most in developing countries. An estimated 1.3 million deaths occurred among HIV -uninfected TB cases and an estimated 456,000 more in HIV -infected TB patients. TB remains a leading infectious cause of death in adults in many low income countries and the leading cause of death among HIV -infected individuals worldwide. The global picture of TB is increasingly complicated by drug resistance and the HIV epidemic (1) .
TB has been recognized as a health problem of returned travellers (2 , 3) . Although the proportion of TB cases in low prevalence nile cruise ship reviews countries which are attributable nile cruise ship reviews to travel is unknown, limited data suggest that in some cases, infection may have been acquired during recent travel to high TB incidence countries (4 - 6) . Because of the long interval between nile cruise ship reviews infection with M. tuberculosis and development of disease, the association with travel-related exposure may be under recognized.
Tuberculosis nile cruise ship reviews is an airborne infection. Droplet nuclei produced by a source individual with active pulmonary TB are inhaled by a susceptible host. The majority of people infected with M. tuberculosis never become symptomatic or ill and are said to have latent tuberculosis infection (LTBI). Overall, it is estimated that approximately 10% of those infected will ultimately develop active tuberculosis with approximately half of that risk in the first one to two years after exposure, the other half being distributed over the remainder of the infected person's life. An individual's risk of progression of infection with M. tuberculosis to active disease is greatly influenced by the presence of other factors; nile cruise ship reviews particularly those affecting nile cruise ship reviews the cell mediated immune response.
The overall risk of a traveller developing active tuberculosis therefore depends on 1) the risk of exposure/infection (refer to Figure 1 ), and 2) the risk of progression to active disease among infected individuals (refer to Table 1 ).
The risk of infection with M. tuberculosis increases with the duration of exposure and is likely to be associated with the degree nile cruise ship reviews of direct contact with local people in a high incidence country and with the conditions of contact, specifically, ventilation and ultraviolet light including sunlight.
The results of the only large prospective study (7) of TB infection nile cruise ship reviews in travellers demonstrated that the risk of infection, defined as conversion of the tuberculin skin test (TST), approximated the risk of transmission in the local population of the destination country. In a retrospective nile cruise ship reviews study, tuberculin positivity was strongly associated with duration of travel to high prevalence countries (8) . A study of returned Peace Corps volunteers showed TST conversion rates intermediate between those of the U.S. population and the rates reported in the study mentioned above (9) .
The annual risk of infection ( TST conversion) varies from 0.5 - 4% per year in low income countries nile cruise ship reviews and correlates approximately with the incidence of smear positive pulmonary TB in the population. Rates of active TB vary widely among different geographic regions of the world. To illustrate the extremes, estimated TB incidence exceeds 1000/100,000 in a few specific communities in Africa (10) , by comparison with less than 1/100,000 among Canadian born non-Aboriginal people. WHO estimated smear positive TB rates for all WHO member nations are available from the Public Health Agency of Canada (PHAC) website and estimates of TB incidence by country can also be obtained online from the World Health Organization (WHO).
Note: a three year average is used to adjust for unstable rates in some jurisdictions. The WHO estimated rates are used, rather than the country/territory reported incidence nile cruise ship reviews rates, as they adjust for under-reporting of cases in some jurisdictions and are more indicative of the current risk of being infected while in the country/territory.
Among specific activities on the part of travellers, working in hospitals in high incidence countries is associated with a particularly high risk. The proportion nile cruise ship reviews of patients presenting to outpatient clinics, emergency departments and medical wards, who have infectious TB is very high in many high incidence countries, especially where HIV is co-endemic. The risk to health care workers, of acquiring M. tuberculosis infection (or active tuberculosis) nile cruise ship reviews has been found to be high in many low income country settings, with tuberculin skin test conversion nile cruise ship reviews as high as 14% per year in a systematic review (11) . In the teaching hospitals of Harare, Zimbabwe where rates of both TB and HIV were very high, the annual incidence of TST conversion in student nurses was 13% (95% CI, 6.5-20.0%) nile cruise ship reviews higher than in an otherwise similar control nile cruise ship reviews group of polytechnic students (12) . Health care work was the only independent risk for TST conversion among the travellers followed by Cobelens, with a risk more than 5 times higher among health care workers than among other travellers (7) .
The risk of TB exposure may also be increased in other settings such as prisons in low income countries, as it is in wealthy countries. In Brazil, the prevalence of active TB in prisoners was 70 fold greater than in the general Brazilian population (13) . Refugees also appear to be associated with a much higher risk of TB than either the source or host populations (14 - 16) implying an increased risk of exposure for those working in refugee nile cruise ship reviews camp settings. Canadian immigrants visiting friends and relatives (VFRs) are likely to represent a group at higher risk, perhaps due to their closer contact with the local population, as several studies have shown an association between TST positivity and return travel to the country of origin (5) , particularly among children (4 , 17 , 18) . Orphanages are not anticipated to be particularly high risk settings since children, even when they have active TB , are less likely to be infectious.
A tourist making a two-week visit to east Africa whose contact is limited to an upscale hotel in the capital city and rural safari camps would be anticipated to have a very low risk of tuberculosis exposure even though the destination country might have a high incidence of TB .
The risk of transmission of TB on all large commercial jet aircraft is very low in part due to the fact that air is exchanged and filtered approximately nile cruise ship reviews 20 times per hour during cruising, with lower exchange rates during descent and while on the ground (19) . When TB contact tracing has been done on commercial air passengers due to exposure to an active case of TB on the same flight, only a few cases of infection with M. tuberculosis are thought to have been acquired (20) , but no active case attributable to travel on a commercial aircraft has been recognized nile cruise ship reviews to date (19) . The greatest risk of acquiring TB on an aircraft appears to be on flights of 8 hours duration and for those sitting within 2 rows of the index case (19 , 21) .
HIV infection is the risk factor most strongly associated with progression of Mycobacterium tuberculosis infection to active TB ; the absolute risk is estimated at ~10%/year, greatest in those with advanced immune suppression and partially reduced by antiretroviral therapy (22 - 24) . Organ transplantation and immune suppressive treatments including new agents such as blockers of tumour necrosis factor (TNF) alpha (25) , depending on the degree nile cruise ship reviews of immune suppression, along with silicosis and chronic renal failure, also substantially increase the risk of TB reactivation. Other, relatively common conditions such as diabetes, cigarette smoking, chest X-ray evidence of prior TB infection and being less than 90% of ideal body weight are associated with increased risk of reactivation, albeit to a lesser degree (refer to Table 1 ).
Several strategies have been proposed for the prevention of TB in travellers. In order for any TB prevention intervention in travellers to be feasible and as cost effective as possible, nile cruise ship reviews it must be strictly targeted to those at highest risk of exposure (high TB incidence in the destination nile cruise ship reviews country, longer duration of stay, and specific activities, particularly health nile cruise ship reviews care work) or at markedly increased risk of progressing to active disease if infected (i.e., immune suppression). Children, particularly 5 years of age, sho