Epidemiologic and economic burden of influenza in the outpatient setting: a prospective study in a subtropical area of China.
OBJECTIVE
To understand the incidence of outpatient influenza cases in a subtropical area of China and the associated economic burden on patients' families.


METHODS
A hospital-based prospective study was conducted in Zhuhai City during 2008-2009. All outpatient influenza-like illness (ILI) cases were identified in 28 sentinel hospitals. A representative sample of throat swabs from ILI cases were collected for virus isolation using Madin-Darby canine kidney cells. The incidence of outpatient influenza cases in Zhuhai was estimated on the basis of the number of influenza patients detected by the sentinel sites. A telephone survey on the direct costs associated with illness was conducted as a follow-up.


RESULTS
The incidence of influenza was estimated to be 4.1 per 1,000 population in 2008 and 19.2 per 1,000 population in 2009. Children aged <5 years were the most-affected population, suffering from influenza at the highest rates (34.3 per 1,000 population in 2008 and 95.3 per 1,000 population in 2009). A high incidence of 29.2-40.9 per 1000 population was also seen in young people aged 5-24 years in 2009. ILI activity and influenza virus isolations adopted a consistent seasonal pattern, with a summer peak in July 2008 and the longest epidemic period lasting from July-December 2009. The medical costs per episode of influenza among urban patients were higher than those for rural patients. A total of $1.1 million in direct economic losses were estimated to be associated with outpatient influenza during 2008-2009 in Zhuhai community.


CONCLUSIONS
Influenza attacks children aged <5 years in greater proportions than children in other age groups. Seasonal influenza 2008 and Pandemic influenza A (H1N1) 2009 had different epidemiological and etiological characteristics. Direct costs (mostly medical costs) impose an enormous burden on the patient family. Vaccination strategies for high-risk groups need to be further strengthened.
Institute of Infectious Disease Prevention and Control, Center for Disease Control and Prevention of Guangdong Province, Guangzhou, China.
Ru-ning
RN
Guo
Hui-zhen
HZ
Zheng
Li-qun
LQ
Huang
Yong
Y
Zhou
Xin
X
Zhang
Chan-kun
CK
Liang
Jin-yan
JY
Lin
Jian-feng
JF
He
Jin-qing
JQ
Zhang
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000818:Animals; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D017281:Cost of Illness; D004285:Dogs; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification / Q000502:physiology; D007251:Influenza, Human / Q000191:economics* / Q000453:epidemiology* / Q000821:virology; D061985:Madin Darby Canine Kidney Cells; D008875:Middle Aged; D010045:Outpatients / Q000706:statistics & numerical data*; D011446:Prospective Studies; D013048:Specimen Handling; D014329:Tropical Climate; D055815:Young Adult