title: Hospital-based influenza surveillance in Korea: hospital-based influenza morbidity and mortality study group.
abstract: Influenza epidemics occur annually with variations in size and severity. Hospital-based Influenza Morbidity & Mortality was established to monitor influenza epidemics and their severity, which is composed of two surveillance systems: emergency room-based and inpatient-based surveillance. Regarding emergency room-based surveillance, influenza-like illness index (influenza-like illness cases per 1,000 emergency room-visiting subjects), number of laboratory-confirmed cases and the distribution of influenza types were estimated weekly. Inpatient-based surveillance included monitoring for hospitalization, complications, and mortality. The emergency room influenza-like illness index correlated well with the number of laboratory-confirmed influenza cases, and showed a bimodal peak at Week 4 (179.2/1,000 emergency room visits) and Weeks 13-14 (169.6/1,000 emergency room visits) of 2012. Influenza A was the predominant strain during the first epidemic peak, while influenza B was isolated exclusively during the second peak. In 2011-2012 season, the mean admission rate of emergency room-visiting patients with influenza-like illness was 16.3% without any increase over the epidemic period. Among the hospitalized patients with influenza, 33.6% (41 out of 122 patients) were accompanied by complications, and pneumonia (28.7%, 35 out of 122 patients) was the most common. Most fatal cases were caused by influenza A (96.2%) after the first epidemic peak. In conclusion, Hospital-based Influenza Morbidity & Mortality was effective for monitoring the trends in circulating influenza activity concurrently with its severity. In the 2011-2012 season, the influenza epidemic persisted for a ≥ 5-month period, with a bimodal peak of influenza A and B in sequence. Overall, influenza A was more severe than influenza B.
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, Korea University College of Medicine, Seoul 152-703, Korea.
authors.forename: Joon Young
authors.initials: JY
authors.lastname: Song
authors.forename: Hee Jin
authors.initials: HJ
authors.lastname: Cheong
authors.forename: Sung Hyuk
authors.initials: SH
authors.lastname: Choi
authors.forename: Ji Hyeon
authors.initials: JH
authors.lastname: Baek
authors.forename: Seung Baik
authors.initials: SB
authors.lastname: Han
authors.forename: Seong-Heon
authors.initials: SH
authors.lastname: Wie
authors.forename: Byung Hak
authors.initials: BH
authors.lastname: So
authors.forename: Hyo Youl
authors.initials: HY
authors.lastname: Kim
authors.forename: Young Keun
authors.initials: YK
authors.lastname: Kim
authors.forename: Won Suk
authors.initials: WS
authors.lastname: Choi
authors.forename: Sung Woo
authors.initials: SW
authors.lastname: Moon
authors.forename: Jacob
authors.initials: J
authors.lastname: Lee
authors.forename: Gu Hyun
authors.initials: GH
authors.lastname: Kang
authors.forename: Hye Won
authors.initials: HW
authors.lastname: Jeong
authors.forename: Jung Soo
authors.initials: JS
authors.lastname: Park
authors.forename: Woo Joo
authors.initials: WJ
authors.lastname: Kim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D062665:Epidemiological Monitoring; D005260:Female; D006761:Hospitals; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D009980:Influenza A virus / Q000302:isolation & purification; D009981:Influenza B virus / Q000302:isolation & purification; D007251:Influenza, Human / Q000150:complications / Q000453:epidemiology* / Q000401:mortality / Q000473:pathology; D007723:Korea / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012720:Severity of Illness Index; D016019:Survival Analysis; D055815:Young Adult