Influenza B Outbreak on a Cruise Ship off the Sao Paulo Coast, Brazil

Background. In February 2012, crew and passengers of a cruise ship sailing off the coast of Sao Paulo, Brazil, were hospitalized for acute respiratory illness (ARI). A field investigation was performed to identify the disease involved and factors associated. Methods. Information on passengers and crew with ARI was obtained from the medical records of hospitalized individuals. Active case finding was performed onboard the ship. ARI was defined as the presence of one nonspecific symptom (fever, chills, myalgia, arthralgia, headache, or malaise) and one respiratory symptom (cough, nasal congestion, sore throat, or dyspnea). A case-control study was conducted among the crew. The cases were crew members with symptoms of influenza-like illness (ILI) (fever and one of the following symptoms: cough, sore throat, and dyspnea) in February 2012. The controls were asymptomatic crew members. Results. The study identified 104 ARI cases: 54 (51.9%) crew members and 50 (49.1%) passengers. Among 11 ARI hospitalized cases, 6 had influenza B virus isolated in nasopharyngeal swab. One mortality among these patients was caused by postinfluenza Staphylococcus aureus pneumonia. The crew members housed in the two lower decks and those belonging to the 18- to 32-year-old age group were more likely to develop ILI [odds ratio (OR) = 2.39, 95% confidence interval (CI) 1.09-5.25 and OR = 3.72, CI 1.25-11.16, respectively]. Conclusions. In February 2012, an influenza B outbreak occurred onboard a cruise ship. Among crew members, ILI was associated with lower cabin location and younger age group. This was the first influenza outbreak detected by Brazilian public health authorities in a vessel cruising in South American waters.