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To the Editor-in-Chief

In their brief communication “The incidence of HBV and HCV infection in Australian travelers,” Johnson et al. calculated the incidence of acute HBV and HCV infection based on seroconversions in paired serum samples tested in a convenience sample of travelers from a study that was set up to calculate the incidence of dengue infections in these travelers. The authors found one seroconversion for HBV and two for HCV and calculated an incidence of 2.19 (95% CI 0.07–12.19) and 1.8 (0.22–6.53) per 10,000 traveler days, respectively.[1] In the same issue of this journal, Johnson et al. report these incidences in their review “Hepatitis B and C infection in international travelers.”[2]

In the discussion of their brief communication, the authors argue that the incidences they found may be underestimations. What the authors did not discuss is that the calculated incidences may very well be overestimations. The one traveler diagnosed with acute hepatitis B was tested 32 days before travel, spent 22 days traveling in China and was tested again 8 days post-travel, 30 days after the start of his journey. He seroconverted for anti-HBc and anti-HBs but was anti-HBc-IgM, HBsAg, and HBV-DNA negative, all indicative for recent infection. The incubation period of hepatitis B is 30 to 180 days, anti-HBc is first detectable about 2 months after infection, and anti-HBs is detectable about 5 months after infection.[3] Seeing the incubation time of hepatitis B and the serologic course of acute hepatitis B infection, it is very unlikely that he acquired this infection during his trip to China and more likely that he was already infected in Australia, making the incidence of hepatitis B in this cohort of travellers, 0.

The mean incubation period for hepatitis C is 50 days (range 14–120 days) and anti-HCV antibodies are detectable as early as 8 weeks after infection. As many as 85% of acutely infected persons develop chronic infection.[3] Two women, who traveled for 2 weeks only, seroconverted for HCV. Unfortunately, the authors do not mention the time between their return to Australia and the second blood samples. Assuming that this was at most a few weeks only, it is unlikely that they were infected during travel as they had already developed anti-HCV antibodies and the virus appeared not to be detectable. As the majority of people who contract hepatitis C become chronically infected, it is also remarkable that in none of the four travelers who tested antibody positive, the virus was detected. The authors therefore should have discussed the specificity of the test they used.

We conclude that the calculated incidences should be interpreted with great care. The study design may have been appropriate to study the incidence of dengue infection but not for calculating the incidence of HBV and HCV. First, dengue is not endemic in the regions of Australia where the participants live, so detected infections must have been contracted during travel, whereas HBV and HCV can be contracted in Australia. Second, the incubation period of dengue is only 4 to 10 days. Third, epidemiological data about possible exposures should have been collected in order to determine whether infections are acquired during travel or while in Australia.

Even though many national guidelines advise to consider hepatitis B vaccination for all travelers, it remains important to stratify travelers according to risk for those countries who advise hepatitis B vaccination to risk groups only. Reliable risk estimations remain important also for travelers who cannot afford all available vaccinations and for whom choices have to be made.

  • Gerard J.B. Sonder* and Anneke van den

  • Hoek*†

  • *National Coordination Center for Travelers Health

  • Advice (LCR), Amsterdam, The Netherlands;

  • Department of Infectious Diseases, Public Health

  • Service, Amsterdam, The Netherlands

References

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