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Studies from around the world show, overall, that although knowledge of STDs is increasing amongst travellers, our level of knowledge has little to do with our actual behaviour; being better informed resulting in only a modest increase in the use of condoms or the practice of self-control, whereas there is abundant evidence that a wide variety of risky and sometimes fatal sexual behaviours is carried out by people who, to use the old cliché, "ought to know better".

Many diseases are known to be spread by sexual contact, more than most people will be aware of: as well as bacterial diseases such as chlamydia, gonorrhoea, syphilis and many others which can usually be cured albeit with difficulty, there are the viral infections (=essentially untreatable); venereal warts, hepatitis A, B, C, D, and herpes; and as well as crabs and scabies there are parasitic infections such as amoebic and giardia infections, and approximately 20 other diseases.

In developing countries, syphilis is common; figures vary from 5-20% in women attending antenatal clinics, to 70% in certain groups, e.g., prostitutes. Syphilis is however often undiagnosed. Gonorrhoea is equally common and while easier to suspect and therefore diagnose, is becoming increasingly difficult to treat due to drug resistance. Non-gonococcal urethritis in men is caused by chlamydia C trachomatis in at least 40% of cases; the female counterpart to NGU frequently causes pelvic inflammatory disease. Chlamydia is harder than gonorrhoea to diagnose and treat.

There is virtually no published data on herpes in developing countries, although based on the studies that have been done it probably accompanies other STDs in at least 20% of cases. Venereal warts are probably three times as common and their key consequence, cervical cancer, is more severe. Most women's partners are also infected, usually sub-clinically; so wart - human papilloma virus (HPV) - infections of the genital tract are probably the most prevalent STD.

Chancre is endemic in many developing countries, particularly in SE Asia, eastern and Southern Africa, and Papua New Guinea, and is as unpleasant as it sounds. Prostitutes play an important role in its spread. Most genital ulcers are due to chancroid, though mixed infections are common.

Viral infections principally affecting the liver, are among the STDs with the highest incidence world-wide.

The most important of these is hepatitis B virus (HBV), estimated to be responsible for chronic infection in at least 300 million individuals, and is the ninth major cause of premature mortality. 75% of these carriers live in Asia and the Far East. Sexual activity is one of the most common forms of HBV transmission; estimates are that 1 in 2,500 travellers and expatriates from developed countries return home with sexually-acquired hepatitis B, most (64%) of these persons working in developing countries rather than travelling for pleasure.

Fortunately, HBV is the first hepatitis virus against which a vaccine has been developed, and indeed the first sexually transmitted disease against which there is an effective vaccine. Recently, preliminary evidence has been forthcoming to suggest that a hitherto - unsuspected route of transmission, viz via bed bugs, may be important. If proven, this would represent a (semi-) sexual route of transmission.

Hepatitis A virus (HAV) is spread by the faecal-oral route, and sexual transmission among homosexual men represents an increased risk.

Hepatitis C virus is also transmitted by sexual contact.

HIV / AIDS: Sexual transmission of HIV accounts for about three quarters of all infections world-wide. The majority have been through heterosexual transmission.

There are three patterns of HIV transmission.

Pattern 1 is predominant in North America, Western Europe, Australia and New Zealand. In pattern 1, sexual transmission occurs principally among homosexual and bisexual men, but heterosexual transmission also occurs and appears to be increasing. Transmission through blood occurs principally as a result of injecting drug use. Perinatal infection is less common because relatively few women in these areas have been infected thus far.

Pattern 2 is found in sub-Saharan Africa, and increasingly in Latin America and the Caribbean. Sexual transmission is predominantly heterosexual, while transmission via contaminated blood transfusion continues in areas where the screening of blood is not yet routine, and perinatal transmission is a major problem since, in some cities, at least 5 to 15% of pregnant women are infected.

Pattern 3 areas include North Africa, the Middle East, Eastern Europe, Asia (but see below) and the Pacific. These areas until recently accounted for only a small proportion of AIDS cases reported. Initial cases resulted from contact with people in Pattern 1 or 2 areas, or from exposure to imported blood. However, indigenous transmission of HIV-1 infection is increasing, especially among prostitutes and drug users. Indeed, it is becoming apparent that India and South East Asia are poised on the brink of a major epidemic, probably of the same order of magnitude as sub-saharan Africa. This exceptionally rapid spread makes for a large infected but not yet actively sick population (i.e., "larger iceberg, smaller tip").

Deaths of international travellers and workers are commonly due to traffic accidents, where blood transfusion might be necessary as a life-saving measure. In the USA, approximately 1 million persons are transfused annually, with each person receiving an average of 2.9 units of blood. If these figures were applied to a typical international trip, the number of persons requiring transfusion would be 1.3 per 10,000 per 2-week period. A number of factors contribute to unsafe operation and limited screening of donated blood and even in countries where blood screening is routine and efficient, but where HIV seroprevalence is increasingly rapidly e.g. Thailand, the theoretical risk of transfusing blood from an HIV-seronegative but viraemic donor in the "window period" of infection has increased greatly; in Chiang Mai (Thailand) the risk of receiving infected blood during this window period has been estimated at 1:200.

The association between travel and STDs has been known for centuries, particularly for syphilis, and it has both been traditional and accurate to blame foreigners, usually sailors and armies. For example, Christopher Columbus's sailors allegedly brought syphilis to Europe, having acquired the infection during their first trip to America in 1492 after intercourse with Haitian women, and Captain James Cook was concerned with the spread of venereal disease, especially during his third voyage (1776-9), when almost half the ship's company had been infected before departure.

Accurate contact tracing is occasionally feasible; an often quoted example is that of a Californian prostitute, nicknamed 'syphilis Mary', who had secondary syphilis; she kept a diary which helped trace 168 long-distance truck drivers among her 310 'regulars' in 34 American states, Canada, and Mexico.

In England and Wales, during the last year for which data are available, 14% of cases of early syphilis were contracted abroad. In Singapore, a country in which the reporting system is particularly robust, 88.9% of gonococcal infections in heterosexual men from 1991-9 were acquired elsewhere in Asia. In Sydney, 64% of heterosexually acquired gonorrhoea in males in the years 1981-1989 was an Asian strain, of which half was acquired outside the country.

Rates of infection among prostitutes are a clear reason for the heterosexual transmission of HIV in any area in the world. Infection rates from 6-90% have been recorded among female prostitutes in urban areas of central, eastern, and southern Africa, and 3-60% in parts of Asia.

In two studies of businessmen being briefed before assignments abroad, there was mostly correct knowledge about general risk factors for AIDS, but only 25% requested more information, even if 30% did not know AIDS was present in the country they were visiting; and only 10% said they would purchase condoms abroad. As above, an important conclusion emerged that has since been confirmed many times, viz. despite adequate knowledge of sexual transmission of HIV, many of us perceive no personal risk of acquiring the disease. This is dangerous.

In Canada, as recently as 1991, 14% of 331 business travellers did not think that avoiding sexual intercourse was protective, and many thought that condoms were more effective if used with fellow travellers than with locals.

In a study of Australians travelling to S-E Asia, only 34% reported a definite intention not to have sex. Less than 60% of those who intended to have sex said they would use condoms 100% of the time(!) These travellers did not perceive a higher personal risk of acquisition of AIDS in Asia than in Australia, even though they were aware of the magnitude of the difference in prevalence. Other studies have confirmed that while condoms are used by over 90% of travellers and workers some of the time, only about 50% use condoms all of the time.

ALL OF THIS MEANS THAT ..

• You can virtually eliminate your risk of STDs or HIV infection if you avoid penetrative sexual intercourse with casual partners, especially injecting drug users and persons who have had multiple sexual partners (such as prostitutes).

• If you still want despite the risks to practice non-monogamous sexual activity, or sexual activity with multiple partners, it is foolish, inconsiderate and dangerous to do so without a condom whatever type of sex (oral, vaginal, anal) is practised. And while you can reduce risks by the use of condoms, some risk will remain.

• Post-travel checks for STDs (including HIV) are essential even if you don't have symptoms, if you have been exposed to high-risk individuals or been active in high risk behaviours. This is best done in developed countries at centres specialising in genitourinary medicine.

HIV/AIDS - adult prevalence rate:
0.1% (2003 est.)

HIV/AIDS - people living with HIV/AIDS:
110,000 (2003 est.)

HIV/AIDS - deaths:
2,400 (2003 est.)

Our appreciation to Dr. Rene de Jongh of International SOS, An AEA Company who has contributed this article in response to a growing health threat faced by expatriate men in Indonesia and Southeast Asia. Statistics show that 1 in 6 prostitues in Thailand are infected with HIV. Closer to home, 3 out of 1,000 expatriate men leave their assignment in Indonesia with HIV. The precautions recommended are based on clinical experience.