When Did They Travel and For How Long

A precise history of timing of travel is essential for comparison with the known incubation periods of specific illnesses, some of which are summarised in Table 12.2.

In the clinic consultation, it is rarely as easy as one might expect to correlate exposure dates with illness in individual patients. In this situation, incubation periods are most useful for excluding illness. For example, malaria does not present in travellers less than 8 days after arriving in a malarious area. Viral haemorrhagic fever can safely be excluded in a patient who has had possible exposure, but has left an endemic area more than 21 days before the onset of symptoms. In epidemic situations or outbreaks clearly related to a point source, knowledge of precise travel and exposure times is very helpful, such as locating a patient within a known outbreak of Legionnaires' disease on a cruise ship or in a specific hotel, or identifying a person as being part of a point source outbreak of food-borne salmonellosis at a wedding reception on the other side of the country. Such examples emphasise both the use of the travel history to inform the diagnosis of the patient and the need for rapid notification of suspected and confirmed diagnoses to the appropriate public health authorities or surveillance scheme, so that patterns of illness and outbreaks can be recognised and disseminated back to the health care community.

At the other end of the scale, disease with long incubation periods may not be recognised as travel-related by either the patient or physician. Hepatitis B transmitted by tattoo during an overland trip through Asia might not cause illness until 6 months later. The increased risk of tuberculosis in immigrants persists for at least 5 years after arrival in Britain (Ormerod, 2000) and the clinical incubation period of symptomatic leprosy is several years. We have seen patients with colonic bleeding due to schistosomiasis presenting for the first time 10 years after travel to Africa. Some infections can persist for many years, such as strongyloidiasis, which we still see in ex-prisoners of war who worked over 50 years ago on the Thai-Burma railway during World War II (Gill and Bell, 1979; Archibald et al., 1993). Knowledge of the biology of the pathogen can also be integrated with the detailed travel history to recognise the limitation of investigation at different phases of the illness.

Table 12.2 Sample incubation periods

Short ( < 10 days)

Medium (10-21 days)

Long ( > 21 days)

Very long

Amoebiasis (intestinal)

Amoebiasis

Amoebic liver abscess

AIDS/symptomatic HIV

Anthrax (pulmonary)

Arboviral infections (few)

Babesiosis

Amoebic liver abscess

Arboviral

Murray Valley fever

Bartonellosis

Chagas' disease

Japanese encephalitis

Encephalitis

Brucellosis

Leprosy

Dengue fever

St Louis

Cytomegalovirus

Leishmaniasis

Yellow fever

Tick-borne

Filariasis

Melioidosis

Babesiosis

Japanese

Hepatitis (A-E)

Neurocysticercosis

Bacterial meningitis

Babesiosis

HIV infection (acute)

Schistosomiasis

Brucellosis

Brucellosis

Infectious mononucleosis

Strongyloidiasis

Campylobacter enteritis

Cytomegalovirus

Leishmaniasis (visceral)

Tuberculosis

Diphtheria

Haemorrhagic fevers

Lyme disease

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