RATES OF HOSPITALIZATION FOR RESPIRATORY DISEASE AMONG CHILDREN WITH NO UNDERLYING CONDITIONS DURING INFLUENZA SEASONS

Chiu SS¹, Lau YL¹, Peiris M².

¹ Department of Paediatrics, Queen Mary Hospital, University of Hong Kong

² Department of Microbiology, Queen Mary Hospital, University of Hong Kong

Objective: To determine the effect of influenza on hospitalization for acute respiratory disease (ARD) in children in Hong Kong where there are more distinct RSV and influenza seasons.

Methods: We performed a retrospective population-based study of children 15 years or younger. Data were retrieved from the Hospital Authority (HA) Head Office. HA hospitals account for 90% of all admissions in Hong Kong. The record of a patient from birth to15 years of age was eligible for inclusion if the discharge code of ARD, 460-466 or 480-487 (International Classification of Diseases, 9th Revision, Clinical Modification) and if the admission to the hospital occurred between January 1998 and December 2000. To calculate the morbidity attributable to influenza, we compared mean hospitalization rates during high influenzavirus activity with that when neither RSV nor influenza had high activity. Influenza A virus and respiratory syncytial virus identified by immunofluorescence in the nasopharyngeal aspirate (NPA) specimens performed at the Queen Mary Hospital (QMH) virology laboratory provided information to define peak viral activity by week during the study period.

Results: During the periods in which influenza predominated, weekly hospitalization rates for ARD among children without high risk were 287.52/100,000 population <1 year of age, 149.61/ 100,000 population 1 year to <2 years of age, 71.23/100,000 population 2 to < 5 years of age, 16.60/100,000 population 5 to <10 years of age and 3.83/100,000 population 10-15 years of age. During the periods in which influenza predominated, excess hospitalization rates for ARD among children without high risk were 97.39/100,000 population <1 year of age, 61.53/100,000 population 1 year to <2 years of age, 29.17/100,000 population 2 to under 5 years of age, 12.43/100,000 population 5 to <10 years of age and 3.52/100,000 population 10-15 years of age.

Conclusion: Infants and children without underlying risk for serious influenza complications are still at increased risk for hospitalization for ARD during influenza season.

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