title: Retrospective investigation of an influenza A/H1N1pdm outbreak in an Italian military ship cruising in the Mediterranean Sea, May-September 2009.
abstract: BACKGROUND
  Clinical surveillance may have underestimated the real extent of the spread of the new strain of influenza A/H1N1, which surfaced in April 2009 originating the first influenza pandemic of the 21(st) century. Here we report a serological investigation on an influenza A/H1N1pdm outbreak in an Italian military ship while cruising in the Mediterranean Sea (May 24-September 6, 2009).
  
  
  METHODS
  The contemporary presence of HAI and CF antibodies was used to retrospectively estimate the extent of influenza A/H1N1pdm spread across the crew members (median age: 29 years).
  
  
  RESULTS
  During the cruise, 2 crew members fulfilled the surveillance case definition for influenza, but only one was laboratory confirmed by influenza A/H1N1pdm-specific RT-PCR; 52 reported acute respiratory illness (ARI) episodes, and 183 reported no ARI episodes. Overall, among the 211 crew member for whom a valid serological result was available, 39.3% tested seropositive for influenza A/H1N1pdm. The proportion of seropositives was significantly associated with more crowded living quarters and tended to be higher in those aged <40 and in those reporting ARI or suspected/confirmed influenza A/H1N1pdm compared to the asymptomatic individuals. No association was found with previous seasonal influenza vaccination.
  
  
  CONCLUSIONS
  These findings underline the risk for rapid spread of novel strains of influenza A in confined environment, such as military ships, where crowding, rigorous working environment, physiologic stress occur. The high proportion of asymptomatic infections in this ship-borne outbreak supports the concept that serological surveillance in such semi-closed communities is essential to appreciate the real extent of influenza A/H1N1pdm spread and can constitute, since the early stage of a pandemic, an useful model to predict the public health impact of pandemic influenza and to establish proportionate and effective countermeasures.
authors.affiliation: Inspectorate of Health, ITA Navy, Rome, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Tarabbo
authors.forename: Daniele
authors.initials: D
authors.lastname: Lapa
authors.forename: Concetta
authors.initials: C
authors.lastname: Castilletti
authors.forename: Pietro
authors.initials: P
authors.lastname: Tommaselli
authors.forename: Riccardo
authors.initials: R
authors.lastname: Guarducci
authors.forename: Giuditta
authors.initials: G
authors.lastname: Lucà
authors.forename: Alessandro
authors.initials: A
authors.lastname: Emanuele
authors.forename: Onofrio
authors.initials: O
authors.lastname: Zaccaria
authors.forename: Vincenzo F P
authors.initials: VF
authors.lastname: La Gioia
authors.forename: Enrico
authors.initials: E
authors.lastname: Girardi
authors.forename: Maria R
authors.initials: MR
authors.lastname: Capobianchi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Ippolito
mesh_terms: D000328:Adult; D000914:Antibodies, Viral / Q000032:analysis; D004196:Disease Outbreaks; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission; D007558:Italy; D008522:Mediterranean Sea; D008889:Military Personnel; D012189:Retrospective Studies; D012306:Risk; D012767:Ships; D013997:Time Factors
chemical_list: D000914:Antibodies, Viral