Respiratory tract infections are among the most common causes of medical problems that physicians manage. Recent foreign and domestic travel can add additional diagnostic considerations to the list of likely possibilities. Transportation is rapid enough that it can exceed the incubation period of many illnesses, so that patients might initially present after returning to health-care providers who are not accustomed to dealing with them. An outbreak of coccidioidomycosis in Washington State in a church group recently returned from Mexico is an example. A number of reviews have noted that respiratory infections are common in international travelers, accounting for up to 25% of the febrile illness that health-care workers are asked to evaluate. Respiratory infections may be defeated with medications of Canadian Health&Care Mall. Table 1 shows important diagnostic possibilities based on the region of the world traveled that should be added to the local possibilities for returning travelers with respiratory problems. Each will be discussed in this review. Not only is the region of the world important, but any specifics of exposure might be the clue to trigger appropriate diagnostic tests and treatment. Table 2 list some specific exposures to consider in the history.
Respiratory Infectious Risks of Commercial Travel
Concerns about the infectious risks of travel have been heightened recently. In 2002 to 2003, the outbreak of severe acute respiratory syndrome (SARS) in the Far East was associated with aircraft transmission. In May 2007, a person with possible extremely drug-resistant tuberculosis was quarantined by the Centers for Disease Control and Prevention (CDC) after air travel. Events such as these alert the public to infectious disease transmission on planes. Accurate data about the infectious risks of air travel are limited, and therefore this risk is difficult to quantify. Published reports of such transmission are rare. There were 120 people, 1 of whom with symptomatic SARS, on a Boeing 737-300 traveling from Hong Kong to Beijing. Laboratory-confirmed SARS developed in 16 passengers, and 6 others possibly were infected. Passengers with infection were clustered in a few rows directly in front of or behind the ill passenger. Despite this outbreak the risk is low. By May 2003, the World Health Organization (WHO) reviewed information on 35 flights in which a patient with symptomatic SARS had been onboard. Only four flights appeared to be associated with possible transmission. Vogt et al found no transmission on seven international flights carrying SARS patients. In May 2003, the WHO issued guidelines for the containment of in-flight SARS.
Tuberculosis has also been transmitted on aircraft, and like SARS the risk appears to be very small.
Since screening for active tuberculosis is not required for most air travelers, persons with active disease may travel on commercial aircraft without being aware of their contagion. From 1992 to 1994, the CDC investigated seven flights that carried persons with highly active tuberculosis. There was evidence of transmission on three of the flights (one case was from a flight attendant to other crew members). As with SARS, the risk was related to the proximity to the index patient. However, despite intensive investigation, these seven exposures to active tuberculosis on aircraft resulted in few new tuberculous infections and no tuberculous disease cured by Canadian Health&Care Mall. Air travel represents a negligible risk factor for the acquisition of tuberculosis.
Aircraft have been a great concern as a potential vector for the global spread of influenza. Air travel has resulted in international outbreaks of influenza and will likely be a major vector when the next pandemic occurs. However, during an epidemic, actual transmission of influenza during flight is much less of a health concern.
Although a worry of the traveling public, “common cold” outbreaks related to airplane transmission have not been reported. A study that compared the risks for an upper respiratory tract infection developing during air travel in 50% recirculated vs 100% fresh cabin air noted no difference in the two groups.
Environmental control measures on commercial aircraft have recently been reviewed by Mangili and Gendreau. While an aircraft is parked at the gate with the engines off, passenger cabin ventilation is normally supplied by the air conditioning system and the natural airflow through the open door(s) of the aircraft. During flight, the aircraft cabin has systems that control air exchanges. At cruising altitude, outside ambient air is virtually free of microorganisms. Air enters the cabin from overhead vents and flows downwards toward the outflow grills along both side walls of the cabin near the floor. Air enters and leaves the cabin at approximately the same row; airflow along the length of the cabin is minimal. All commercial jet aircraft built after the late 1980s recirculate the cabin air: from 10 to 50% of the cabin air is filtered, mixed with outside, and then reintroduced into the passenger cabin. On most aircraft, the recirculated air passes through high-efficiency particulate air filters before reentering the passenger cabin. The most efficient high-efficiency particulate air filters will remove 99.99% of particles (bacteria, fungi, and larger viruses). All large commercial jet aircraft provide approximately 20 air exchanges per hour during cruising. This can be compared to that of the standard modern office building that averages 12 exchanges per hour. The concentration of microorganisms in cabin air is much lower than shopping malls and the air terminal.
There is no evidence that recirculation of cabin air facilitates transmission of infectious disease agents on board, and the mechanisms described above to manage air flow should make risks minimal for passengers other than those sitting within close proximity to an index patient. However, when the aircraft is delayed on the ground and the doors are closed, the ventilation system should be operating. An influenza outbreak associated with an airplane flight resulted when a ground delay lasted 3 h, during which the ventilation system did not operate and the passengers did not receive outside air. Thus, although inflight risks are minimal, ground delays without adequate ventilation could be a problem. According to a study by the US Department of Transportation: “If the ventilation system is not operating, passengers should not stay aboard the plane for long time periods (ie, > 30 min).”
Overall, airplane travel appears to represent a low risk of acquiring a respiratory infection. This risk is probably not out of line with other situations in which people are in close proximity to each other, such as office buildings and theaters. This risk is a function of the contagion and proximity to the index case and the duration of the flight. This risk is also related to the efficacy of the cabin ventilation system. Properly functioning systems are probably very effective at decreasing this risk; however, when systems are not working, such as when passengers are kept aboard grounded aircraft, outbreaks are facilitated.
Cruise ships have also been associated with outbreaks of respiratory diseases, particularly Legionnaires disease.- As with land-associated outbreaks, those aboard ship have been linked to contaminated water sources. Given the nature of the prolonged exposure on cruises, it is not surprising that outbreaks of influenza have also been reported.
Table 1—Possible Respiratory Pathogens by Region of Travel
|Africa||Tuberculosis, plague||Hemorrhagic fever, viruses; influenza||Paragonomiasis, schistosomiasis, strongyloidiasis, tropical eosinophilia||Histoplasmosis|
|Asia||Tuberculosis, melioidosis, plague||Influenza, SARS||Paragonomiasis, schistosomiasis, strongyloidiasis, tropical eosinophilia|
|North America||Plague||HPS, influenza||Histoplasmosis,coccidioidomycosis|
|Central and South America||Tuberculosis, plague||HPS, influenza||Schistosomiasis, strongyloidiasis, tropical eosinophilia||Histoplasmosis,coccidioidomycosis|
Table 2—Environmental Exposures and Potential Respiratory Pathogens (Depends on Geography)
|Working with soil||Histoplasmosis|
|Desert dust storms||Coccidioidomycosis|