Epidemiology and Infection



A large outbreak of influenza A and B on a cruise ship causing widespread morbidity


J. M. L. BROTHERTON a1a2c1, V. C. DELPECH a1, G. L. GILBERT a3, S. HATZI a4, P. D. PARASKEVOPOULOS a4, J. M. MCANULTY a1 and on behalf of the Cruise Ship Outbreak Investigation Team
a1 Communicable Diseases Branch, NSW Department of Health, North Sydney 2059, NSW, Australia
a2 NSW Public Health Officer Training Program, Public Health Training and Development Branch, NSW Department of Health, North Sydney 2059, NSW, Australia
a3 Institute of Clinical Pathology and Medical Research, Westmead Hospital, Westmead 2145, NSW, Australia
a4 South Eastern Sydney Public Health Unit, South Eastern Sydney Area Health Service, Randwick 2031, NSW, Australia

Abstract

In September 2000 an outbreak of influenza-like illness was reported on a cruise ship sailing between Sydney and Noumea with over 1100 passengers and 400 crew on board. Laboratory testing of passengers and crew indicated that both influenza A and B had been circulating on the ship. The cruise coincided with the peak influenza period in Sydney. Morbidity was high with 40 passengers hospitalized, two of whom died. A questionnaire was sent to passengers 3 weeks after the cruise and 836 of 1119 (75%) responded. A total of 310 passengers (37%) reported suffering from an influenza-like illness (defined as cough, fever, myalgia and weakness) and 528 (63%) had seen a doctor for illness related to the cruise. One-third of passengers reported receipt of influenza vaccination in 2000; however neither their rates of influenza-like illness nor hospitalization were significantly different from those in unvaccinated passengers. A case–control study also found no significant protective effect of influenza vaccination. With the increasing popularity of cruise vacations, such outbreaks are likely to affect increasing numbers of people. Whilst influenza vaccination of passengers and crew may afford some protection, uptake and effectiveness may not be sufficient to prevent outbreaks. Surveillance systems and early intervention measures, such as antiviral therapies, should be considered to detect and control such outbreaks.

(Accepted November 21 2002)


Correspondence:
c1 Author for correspondence: Public Health Training and Development Branch, NSW Department of Health, LMB 961, North Sydney 2059, NSW, Australia.


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