To the Editor-in-Chief
We read with interest the brief communication that deals with the incidence of hepatitis B virus (HBV) and hepatitis C virus (HCV) infections in travelers, which appeared in the May to June issue of Journal of Travel Medicine. We would like to comment as follows:
Data regarding the prevalence of HBV and HCV infections in travelers returning from developing countries are scarce and are mainly based on limited case reports and case series. In the brief communication by Johnson and colleagues, they present a retrospective calculation of the incidence of HBV and HCV infections in short-term Australian travelers visiting Asia. All cohort cases had pre- and post-travel blood samples drawn.
According to their results, only 1 of 159 non-immune travelers seroconverted to HBV and the incidence was calculated as 2.19 per 10,000 traveler-days. However, there is a mismatch between the given time frame of the trip, the blood sample results, and the conclusion. The pre-travel blood sample was collected 31 days before departure, the trip was 22 days, and the post-travel blood sample was taken 8 days after his return to Australia (Figure 1). Pre-travel blood samples were all negative for HBV workup. Post-travel samples were positive for anti-HBc and anti-HBs. The presence of both serologic markers indicates a resolved infection. Exposure, incubation period, acute disease, and recovery are impossible within 30 days (22 + 8 days), and the exposure could not have been during the travel.
With regard to HCV infection, 2 of 361 patients had HCV seroconversion representing an incidence density of 1.8 new infections per 10,000 traveler-days. In these two cases too, looking at time frame and the available serology, infection during their trip appears to be impossible. They both traveled for 14 days and blood was collected at a median of 6 days post-travel (range: 0–31 days). Only the post-travel sample was positive for anti-HCV, while HCV polymerase chain reaction (PCR) was negative. According to the literature, HCV RNA becomes detectable in the serum within days to 8 weeks following exposure. Anti-HCV tests become positive as early as 8 weeks after exposure. With the given time frame (even if the blood samples were drawn 31 days post-travel) and blood test results, the conclusions that could be driven are that either the travelers were not exposed to HCV during travel or that false-positive results were obtained. Screening test for hepatitis C may give approximately 35% false-positive result in an immunocompetent population; therefore, confirmatory tests, both recombinant immunoblot assay (RIBA) and HCV RNA, are needed. In the cases mentioned above, RIBA test was not done and HCV PCR was negative; altogether this most likely indicates a false-positive anti-HCV result.
In conclusion, the reported cases of hepatitis B and hepatitis C in this study are either incorrect or indeed a seroconversion had occurred but it is not travel related. Therefore, the given incidence density calculations are erroneous. These incorrect numbers are already cited in the review and editorial in the same issue of this journal.[7, 8]