However, given the long incubation period, we were unable to exclude acquisition of acute HBV infection cases prior to travel. Studies of travelers have demonstrated that new sexual partners and unprotected intercourse are relatively common,[24, 26] particularly in the setting of excessive alcohol intake.[27] Prolonged duration

of travel is associated with an increased likelihood of HBV infection. In susceptible expatriates residing in countries of high HBV endemicity, the estimated monthly incidence of HBV infection ranges from 25 per 100,000 LDK378 price for symptomatic infections to 80 to 420 per 100,000 for all HBV infections.[17] Volunteers, aid workers, and missionaries are at increased risk of HBV infection as a result of extended travel and close contact with the local population. A study of North Veliparib clinical trial American missionaries between 1967 and 1984 with prolonged periods abroad (average 7.3 years) in tropical and subtropical regions identified anti-HB

core (anti-HBc) antibody seroconversion in 5.5% of study subjects.[28] A study of Swedish expatriates demonstrated that the prevalence of anti-HBc antibody was 5%, double that of the general population.[19] A Japanese study identified 72 cases of acute HBV infection (0.68%) in 10,509 Japanese volunteers traveling to tropical and subtropical countries between 1978 and 1993. The incidence of HBV infection dropped dramatically following the introduction Cyclic nucleotide phosphodiesterase of vaccination in conjunction with providing education on the risk factors for HBV infection to the volunteers prior to travel.[29] The precise risk for short-term travelers is not known but is estimated to be significantly lower.[16, 17, 30, 31] A study of Danish travelers demonstrated that the monthly incidence of HBV infection was 10.2 per 100,000 with 62% of cases traveling for <4 weeks.[32] Many studies rely on travelers becoming unwell following travel in order for testing to occur

so will underestimate the incidence of HBV infection.[25] We recently reported the incidence of HBV and HCV infection in a retrospective cohort study of 361 Australian travelers to Asia.[33] This cohort was composed of predominantly short-term travelers with a median travel duration of 21 days (range 7–326), 74% of whom traveled for <30 days. Fifty-six percent of the travelers (202 of 361) were HBV immune [anti-HB surface (anti-HBs) antibody ≥ 10 mIU/mL], with the majority (106 of 202) having anti-HBs antibody titers between 10 and 200 mIU/mL. Analysis of pre- and post-travel sera demonstrated HBV seroconversion in a male traveler to China, representing an incidence density of new HBV infections in nonimmune travelers of 2.19 per 10,000 travel days (95% CI: 0.07–12.19). Of note, 59% of HBV nonimmune travelers attended a pre-travel clinic at least 21 days prior to departure to Asia. This would have provided sufficient time for HBV vaccination (accelerated schedule) and indicates a missed opportunity for vaccination.