Contribution of respiratory syncytial virus, influenza and parainfluenza viruses to acute respiratory infections in San Luis Potosí, Mexico.

BACKGROUND: Respiratory viruses are the main pathogens associated with acute respiratory illness (ARI) in children.
OBJECTIVE: To establish the relationship between the presence of respiratory syncytial virus (RSV), influenza and parainfluenza viruses in the community and the number of ARI and pneumonia cases reported to the State Health Services Epidemiology Department (SHSED) in San Luis Potosí, México.
METHODS: We compared the weekly number of ARI and pneumonia episodes in children younger than 5 years of age reported to the SHSED for weeks in which the different respiratory viruses were detected in the community. Excess respiratory infection episodes compared with nonepidemic periods were calculated for each of the viruses.
RESULTS: From July 2003 through June 2004, there were 236,597 ARI episodes and 2350 pneumonia cases reported to the SHSED. Distinct epidemic periods for parainfluenza type 1 and influenza were observed, whereas RSV and parainfluenza type 3 epidemic periods showed some overlap. The weekly number of excess ARI was greatest when influenza circulated in the community, whereas excess pneumonia cases were greatest when RSV was prevalent. Overall RSV was associated to the largest number of excess ARI and pneumonia cases reported to the SHSED.
CONCLUSIONS: RSV detection is associated to the greatest number of ARI and pneumonia episodes in the state of San Luis Potosí. Influenza epidemics are associated to a significant number of ARI visits. Appropriate surveillance systems will be required to assess the impact of influenza immunization and other preventive measures on the number of ARI and pneumonia cases in our community.