Highlights of the 5th International Conference on Travel Medicine

CONFERENCE COVERAGE

Note: The following summaries represent a personal selection of the most interesting clinical papers presented at the meeting held in Geneva, Switzerland, March 24-27, 1997. The meeting, which is organized every two years by the International Society of Travel Medicine, attracted 1300 delegates from more than 50 countries. Data are abstracted both from the published program book and from the presentations themselves.—David O. Freedman, MD

Practice of Travel Medicine

A well-known travel practice in Connecticut reported on changing demographics of its patients by comparing those patients seen since 1990 with those seen between 1984 and 1990 (total, n = 6716). Changes during the later period included a 12% relative decrease in vacation travel and a more than 25% increase in business and study travel, a 114% increase in travel to Central America, a 37% decrease to East Africa, and a 40% increase to Southern Africa. This closely mirrors my own experience and is, in general, healthy for travel clinics as business travel represents a steadier flow of repeat clinic patients when compared to leisure travel.

Emerging Infections

Good news regarding the diphtheria epidemic in the former Soviet Union was conveyed in a report from the World Health Organization (WHO). In response to large infusions of vaccine and financial aid from the international donor community, decreasing numbers of diphtheria cases in almost all the newly independent states are being reported as of early 1996. Clearly, the risk to travelers is still present, but with continuing sustained infrastructure aid from abroad, hopefully the epidemic is on its way to being under control.

David Heymann, chief of WHO’s new emerging pathogens unit, left the audience in momentary stunned silence during his description of the WHO response and investigation capability. He showed a slide, taken three weeks earlier in Zaire, showing a child who appeared to have a classic case of smallpox. The child turned out to have Monkeypox, a related orthopoxvirus, which is enzootic in local monkeys and which had been reported to cause sporadic cases in directly infected humans since 1970. Now, it is clear that there is human-to-human transmission occurring, and the exact extent of the epidemic of this new disease is under investigation. In the February 1997 investigation of 12 villages with about 4000 inhabitants, the attack rate was about 2%. Since the case fatality rate was relatively low at about 3%, the possibility of this infection becoming endemic in the human population is very real.

Typhoid

In a retrospective study conducted in a very large post-travel practice in Germany, risk factors for culture-proven typhoid fever were examined. Infected patients were older (39 vs 31 years for the average traveler seen) and had traveled longer (58 vs 19 days). One-third of the infected patients had traveled to the Indian sub-continent and one-third to Southeast Asia, even though only 20% of the total patient population had traveled to each of these regions. In contrast, Latin America, which, based on still widely quoted data from the 1970s, is thought to present high risk for typhoid, accounted for only 6% of the typhoid cases, even though 16% of the total patient population had visited there.

An outbreak of five cases of typhoid in travelers to a particular hotel in Indonesia yielded some interesting, though not statistically rigorous, data on efficacy of various typhoid vaccines. Of 110 respondents to the survey, all five cases had received a three-capsule regimen of the oral Ty21a vaccine. Sixty-three other travelers without typhoid had also received the oral vaccine, but there were no cases in 20 travelers receiving the Vi polysaccharide vaccine, eight receiving no vaccine, and seven receiving whole-cell vaccine. These data may not be strictly applicable to U.S. practice, where the Ty21a regimen consists of four doses of vaccine, but it certainly causes me to stop and think.

Tick-Borne Encephalitis

Outbreaks of this flavivirus, related to dengue, yellow fever, and West Nile virus, have reached unprecedented levels in central and eastern Europe over the past few years. Areas at risk in the summertime include parts of Germany, Austria, the Baltic states and the former Yugoslavia. No one was able to quote any specific risk for travelers or foreigners, but, even in the absence of data or clinical reports, the risk to travelers appears to be, fortunately, quite low. This may, however, simply reflect the particular endemic areas being off the majority of foreign tourist itineraries. Clinical syndromes include encephalitis and myelitis syndromes, with the latter more likely to result in sequelae. Two major manufacturers are selling record amounts of vaccine, but these products are only available in endemic countries.

Hepatitis

The major news is the commercial availability of a combination hepatitis A & B vaccine (Twinrix, SmithKline Beecham [SKB]) in some European countries, with indications that licensure has been applied for in the United States. It is not clear is if the U.S. formulation will be the same. The European preparation is a 0-, one-, and six-month regimen containing 720 EU of hepatitis A antigen and 20 mcg of hepatitis B antigen. Havrix, the currently available SKB hepatitis A vaccine for adults in the United States, contains 1440 EU of antigen and has a 0- and six-month dosing regimen. While seroconversion rates at one month were extremely impressive for both components of Twinrix, I was unable to find any two-week seroconversion data for the hepatitis A component of Twinrix. This is important to travel medicine practice because most of our patients come in at the last moment and the Havrix 1440 we now use performs extremely well at the two-week time point.

Increasing numbers of cases of hepatitis E and decreasing numbers of cases of hepatitis A are being seen in travelers to areas of Nepal, endemic for both viruses even though infection rates don’t seem to be rising in local populations. One explanation raised for this finding is that hepatitis A is more aggressive than E, but now that the majority of travelers are vaccinated against A, it has given E a chance to flourish in travelers ingesting food and beverage contaminated with both viruses.

Malaria

Several papers on adverse effects of mefloquine reported figures very similar to those that have been in the literature for the past couple of years. One report compared adverse effects when the loading dose regimen of mefloquine was used compared to the standard weekly regimen. No differences in overall rates of adverse effects were found, although, not surprisingly, reactions tended to occur earlier in time in those achieving earlier steady state levels by using the loading dose regimen.

Reports were released on a number of highly experimental malaria chemoprophylactics. Of the drugs that already have clinical efficacy trial data available, the most promising on the horizon are: atovaquone/proguanil (Malarone, Glaxo Wellcome), which is already registered in the United Kingdom for treatment only; azithromycin, which would have to be taken daily; halofantrine (Halfan, SmithKline Beecham), which has a micronized formulation that is said to minimize potential cardiotoxicity; and WR238605, a long-acting primaquine analog that may be able to be used weekly. We clearly need new chemoprophylactics that are easy to take and are acceptable to patients. An analysis of WHO and individual country data from key European countries indicates that between 1985 and 1995 there were between 5000 and 9000 cases of imported malaria in Europe with increasing proportions of P. falciparum and increasing case-fatality rates.