Varicella among seafarers: a case study on testing and vaccination as a cost-effective method of prevention.

BACKGROUND Many individuals together in semi-confined settings increase the risk of outbreaks of infectious diseases. A single case of varicella on a cruise ship can thus result in rapid spread and elevated costs for the cruise provider in terms of repatriation, ship diversion, law suits, and loss in current and potential future revenue. Control of varicella involves attention to good personal hygiene, safe food and water handling, and use of vaccine. OBJECTIVES To test crewmembers during their pre-employment medical examination to determine who might be susceptible to contract varicella if exposed, to vaccinate those at risk, and to see whether the benefits of testing and vaccination outweigh the costs. MATERIAL AND METHODS Tests were conducted on 121 Indian seafarers for varicella IgG and IgM antibodies during their pre-employment medical examination in Mumbai and Goa from December 1st to December 23rd 2008. Cases without IgG antibodies to varicella (IgG negative) were administered vaccine. RESULTS Twenty (16.5%) seafarers who tested IgG negative and one who tested equivocally were administered the vaccine. One hundred (82.7%) tested positive for IgG antibodies and were therefore not vaccinated. None tested positive for IgM antibodies, indicating no active infection. CONCLUSIONS One in six Indian seafarers tested IgG negative and was thus at risk to contract varicella if exposed. Testing for varicella IgG and IgM antibodies, followed by vaccination when necessary, is a costeffective method to prevent an expensive outbreak in the semi-confined setting of a cruise ship and is recommended as a mandatory part of the pre-employment medical examination for Indian seafarers.