Geographic Distribution of Potential Health Hazards to Travellers

Introduction: Goals and Limitations

This section provides information about which disease exposures are likely in different geographic regions of the world. It is intended to help the clinician provide useful region-specific education and other interventions to prospective travellers and assist in the evaluation of ill returned travellers. The data presented here have many limitations. The areas where an infection can be acquired may expand, contract, and shift over time. New diseases are recognised; old ones are sometimes eliminated, although sequelae in individuals may persist after active transmission has ceased. Humans move, sometimes carrying pathogens (and potential for transmission) with them. The data on which these descriptions are based may be incomplete, inaccurate, or out of date. Most infectious diseases are not notifiable; even when reported, the data typically reflect only a small fraction of actual cases. Reports may be withheld, delayed, or modified because of concerns about the economic impact of an infectious disease on travel and trade. Maps of disease distribution are usually based on infections in a local population, yet risk of clinical infection (e.g., hepatitis A or diarrhoea) in a traveller to a region may be substantially higher than in a local resident (most of whom may be immune) or substantially lower (e.g., ascaris, hookworm, or filariasis) because of living conditions and duration of time spent in the area. Manifestations of the same infection in traveller and local resident may differ because of host factors.

Although we use country names to describe areas of risk, distributions of infection typically do not coincide with geopolitical boundaries. Adding to the complexity, countries may be split, boundaries may shift, and names may change, making tracking of data about distribution in a particular region over time more difficult.

Ideally, spatial (location of transmission) and temporal (seasons or years of risk) distribution and intensity of transmission would be displayed. Semiquantitative terms, such as common, uncommon, and rare, used to describe risk of infection have different meanings for different people and are used inconsistently. Portrayal of risk is often influenced by severity or lethality of infection and not just by the numbers of cases.

Host factors, duration of stay, accommodations, and specific activities influence types and level of risk. These summaries represent broad generalisations intended to provide some initial guidance to clinicians.

The information is displayed in different ways. Table 3-1 portrays 24 of the more common infections in travellers and allows a quick overview of disease risks for specific pathogens by region. Respiratory tract and diarrhoeal infections, among the most common infections in travellers, are caused by multiple different pathogens, many with a global distribution. For infections caused by specific pathogens, the level of risk (including history of epidemic activity or high-risk areas) is based on information in local populations. In the summary for each region, important infectious disease risks are described, organized by means of transmission. Those marked by an asterisk (*) within the text have more than one mode of transmission.

The reader should keep in mind that many microbes, such as influenza virus, cytomegalovirus, Epstein-Barr virus, HIV, Toxoplasma, Streptococci, Streptococcus pneumoniae, Salmonella, Neisseria gonorrhoeae, Treponema pallidum (syphilis), Campylobacter, the coliforms causing urinary tract infections, and many others are globally distributed and cause infections in travellers. Travellers may be at increased risk for some of these because of the conditions of travel (e.g., crowding, poor sanitation, and poor air quality) or activities during travel (e.g., sex with new partners). Most of these broadly distributed infections are not described specifically in the regional sections.

Most sections include a comment about more common infections that occur in travellers to the region and also note chronic and latent infections that may be seen in immigrants from the region.

The disease lists are by no means exhaustive. Infections that are preventable and treatable are more likely to be included. The materials in this section are intended to be used in conjunction with other sections of this book that provide maps and give more details about specific infections. Other useful materials can be found on the CDC and WHO websites and from other sources.

Table 3-1. Disease distribution

1Histoplasmosis, coccidioidomycosis, and paracoccidioidomycosis

Key:
L: local transmission documented but rare
S: sporadic, focal, or seasonal transmission in region
W: widespread transmission
H: epidemic activity or high risk for infection in some areas
Blank: No reported cases (Does not necessarily mean that there is no risk)

Key:
L: local transmission documented but rare
S: sporadic, focal, or seasonal transmission in region
W: widespread transmission
H: epidemic activity or high risk for infection in some areas
Blank: No reported cases (Does not necessarily mean that there is no risk)

Key:
L: local transmission documented but rare
S: sporadic, focal, or seasonal transmission in region
W: widespread transmission
H: epidemic activity or high risk for infection in some areas
Blank: No reported cases (Does not necessarily mean that there is no risk)

2Including African trypanosomiasis (sleeping sickness) and American trypanosomiasis (Chagas' disease)