Viral respiratory tract infections among patients with acute undifferentiated fever in Vietnam.

To investigate the proportion of viral respiratory tract infections among acute undifferentiated fevers (AUFs) at primary health facilities in southern Viet- nam during 2001-2005, patients with AUF not caused by malaria were enrolled at twelve primary health facilities and a clinic for malaria control program. Serum was collected on first presentation (t0) and after 3 weeks (t3) for serology. After exclusion of acute dengue infection, acute and convalescent serum samples from 606 patients were using enzyme-linked immunoassays to detect IgA, as well as IgM and IgG antibodies against common respiratory viruses. Paired sera showed the following infections: human parainfluenza virus (HPIV, 4.7%), influenza B vi- rus (FLUBV, 2.2%), influenza A virus (FLUAV, 1.9%) and human respiratory syn- cytial virus (HRSV, 0.6%). There was no association between type of infection and age, sex or seasonality; some inter-annual differences were observed for influ- enza. Antibody prevalence, indicative of previous infections, was relatively low: HPV, 56.8%, FLUBV, 12.1%; FLUAV, 5.9% and HRSV, 6.8%.