title: Seroepidemiology of norovirus-associated travelers' diarrhea.
abstract: BACKGROUND
  Noroviruses (NoVs) are the most common cause of epidemic gastroenteritis, responsible for at least 50% of all gastroenteritis outbreaks worldwide and were recently identified as a leading cause of travelers' diarrhea (TD) in US and European travelers to Mexico, Guatemala, and India.
  
  
  METHODS
  Serum and diarrheic stool samples were collected from 75 US student travelers to Cuernavaca, Mexico, who developed TD. NoV RNA was detected in acute diarrheic stool samples using reverse transcription-polymerase chain reaction (RT-PCR). Serology assays were performed using GI.1 Norwalk virus (NV) and GII.4 Houston virus (HOV) virus-like particles (VLPs) to measure serum levels of immunoglobulin A (IgA) and IgG by dissociation-enhanced lanthanide fluorescent immunoassay (DELFIA); serum IgM was measured by capture enzyme-linked immunosorbent assay (ELISA), and the 50% antibody-blocking titer (BT50 ) was determined by a carbohydrate-blocking assay.
  
  
  RESULTS
  NoV infection was identified in 12 (16%; 9 GI-NoV and 3 GII-NoV) of 75 travelers by either RT-PCR or fourfold or more rise in antibody titer. Significantly more individuals had detectable preexisting IgA antibodies against HOV (62/75, 83%) than against NV (49/75, 65%) (p = 0.025) VLPs. A significant difference was observed between NV- and HOV-specific preexisting IgA antibody levels (p = 0.0037), IgG (p = 0.003), and BT50 (p = <0.0001). None of the NoV-infected TD travelers had BT50  > 200, a level that has been described previously as a possible correlate of protection.
  
  
  CONCLUSIONS
  We found that GI-NoVs are commonly associated with TD cases identified in US adults traveling to Mexico, and seroprevalence rates and geometric mean antibody levels to a GI-NoV were lower than to a GII-NoV strain.
authors.affiliation: Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA; School of Public Health, Center for Infectious Diseases, Houston, TX, USA.
authors.forename: Nadim J
authors.initials: NJ
authors.lastname: Ajami
authors.forename: Owen V
authors.initials: OV
authors.lastname: Kavanagh
authors.forename: Sasirekha
authors.initials: S
authors.lastname: Ramani
authors.forename: Sue E
authors.initials: SE
authors.lastname: Crawford
authors.forename: Robert L
authors.initials: RL
authors.lastname: Atmar
authors.forename: Zhi-Dong
authors.initials: ZD
authors.lastname: Jiang
authors.forename: Pablo C
authors.initials: PC
authors.lastname: Okhuysen
authors.forename: Mary K
authors.initials: MK
authors.lastname: Estes
authors.forename: Herbert L
authors.initials: HL
authors.lastname: DuPont
mesh_terms: D000328:Adult; D003967:Diarrhea / Q000097:blood / Q000453:epidemiology / Q000503:physiopathology / Q000821:virology; D004196:Disease Outbreaks; D005243:Feces / Q000821:virology; D005260:Female; D005759:Gastroenteritis / Q000097:blood / Q000453:epidemiology / Q000503:physiopathology / Q000821:virology; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007136:Immunoglobulins / Q000097:blood; D008297:Male; D008800:Mexico / Q000453:epidemiology; D029322:Norovirus / Q000302:isolation & purification*; D017063:Outcome Assessment, Health Care; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D016036:Seroepidemiologic Studies; D012698:Serologic Tests / Q000379:methods; D014195:Travel; D014481:United States / Q000453:epidemiology
chemical_list: D007136:Immunoglobulins