title: Evidence of cross-reactive immunity to 2009 pandemic influenza A virus in workers seropositive to swine H1N1 influenza viruses circulating in Italy.
abstract: BACKGROUND
  Pigs play a key epidemiologic role in the ecology of influenza A viruses (IAVs) emerging from animal hosts and transmitted to humans. Between 2008 and 2010, we investigated the health risk of occupational exposure to swine influenza viruses (SIVs) in Italy, during the emergence and spread of the 2009 H1N1 pandemic (H1N1pdm) virus.
  
  
  RESULTS
  Serum samples from 123 swine workers (SWs) and 379 control subjects (Cs), not exposed to pig herds, were tested by haemagglutination inhibition (HI) assay against selected SIVs belonging to H1N1 (swH1N1), H1N2 (swH1N2) and H3N2 (swH3N2) subtypes circulating in the study area. Potential cross-reactivity between swine and human IAVs was evaluated by testing sera against recent, pandemic and seasonal, human influenza viruses (H1N1 and H3N2 antigenic subtypes). Samples tested against swH1N1 and H1N1pdm viruses were categorized into sera collected before (n. 84 SWs; n. 234 Cs) and after (n. 39 SWs; n. 145 Cs) the pandemic peak. HI-antibody titers ≥10 were considered positive. In both pre-pandemic and post-pandemic peak subperiods, SWs showed significantly higher swH1N1 seroprevalences when compared with Cs (52.4% vs. 4.7% and 59% vs. 9.7%, respectively). Comparable HI results were obtained against H1N1pdm antigen (58.3% vs. 7.7% and 59% vs. 31.7%, respectively). No differences were found between HI seroreactivity detected in SWs and Cs against swH1N2 (33.3% vs. 40.4%) and swH3N2 (51.2 vs. 55.4%) viruses. These findings indicate the occurrence of swH1N1 transmission from pigs to Italian SWs.
  
  
  CONCLUSIONS
  A significant increase of H1N1pdm seroprevalences occurred in the post-pandemic peak subperiod in the Cs (p<0.001) whereas SWs showed no differences between the two subperiods, suggesting a possible occurrence of cross-protective immunity related to previous swH1N1 infections. These data underline the importance of risk assessment and occupational health surveillance activities aimed at early detection and control of SIVs with pandemic potential in humans.
authors.affiliation: Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy. mariaalessandra.demarco@iss.it
authors.forename: Maria A
authors.initials: MA
authors.lastname: De Marco
authors.forename: Stefano
authors.initials: S
authors.lastname: Porru
authors.forename: Paolo
authors.initials: P
authors.lastname: Cordioli
authors.forename: Bruno M
authors.initials: BM
authors.lastname: Cesana
authors.forename: Ana
authors.initials: A
authors.lastname: Moreno
authors.forename: Laura
authors.initials: L
authors.lastname: Calzoletti
authors.forename: Lebana
authors.initials: L
authors.lastname: Bonfanti
authors.forename: Arianna
authors.initials: A
authors.lastname: Boni
authors.forename: Antonio Scotto
authors.initials: AS
authors.lastname: Di Carlo
authors.forename: Cecilia
authors.initials: C
authors.lastname: Arici
authors.forename: Angela
authors.initials: A
authors.lastname: Carta
authors.forename: Maria R
authors.initials: MR
authors.lastname: Castrucci
authors.forename: Isabella
authors.initials: I
authors.lastname: Donatelli
authors.forename: Paola
authors.initials: P
authors.lastname: Tomao
authors.forename: Vittoria M
authors.initials: VM
authors.lastname: Peri
authors.forename: Livia
authors.initials: L
authors.lastname: Di Trani
authors.forename: Nicoletta
authors.initials: N
authors.lastname: Vonesch
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood* / Q000276:immunology*; D000956:Antigens, Viral / Q000276:immunology; D003429:Cross Reactions / Q000276:immunology*; D005260:Female; D006801:Humans; D007109:Immunity / Q000276:immunology*; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D057221:Influenza A Virus, H1N2 Subtype / Q000276:immunology; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure / Q000706:statistics & numerical data*; D058873:Pandemics / Q000706:statistics & numerical data*; D012621:Seasons; D013552:Swine / Q000821:virology*; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D000956:Antigens, Viral