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Volume 16, Number 11—November 2010

Dispatch

Estimates of the True Number of Cases of Pandemic (H1N1) 2009, Beijing, China

Xiaoli Wang, Peng Yang, Holly Seale, Yi Zhang, Ying Deng, Xinghuo Pang, Xiong He, and Quanyi WangComments to Author 
Author affiliations: Beijing Center for Disease Prevention and Control, Beijing, People’s Republic of China (X. Wang, P. Yang, Y. Zhang, Y. Deng, X. Pang, X. He, Q. Wang); Capital Medical University School of Public Health and Family Medicine. Beijing (X. Wang, P. Yang, Y. Zhang, Y. Deng, X. Pang, X. He, Q. Want); University of New South Wales, Sydney, New South Wales, Australia (H. Seale)

Main Article

Table 1

Parameter values and sources of data included in the multiplier model for estimating the true number of persons infected with pandemic (H1N1) 2009, Beijing*†

Code Parameter Value, % Source
A Proportion of symptomatic infection among case-patients with pandemic (H1N1) 2009 70–75 Pandemic (H1N1) 2009, ECDC Risk Assessment.,2009; version 6, 6 Nov.
B Proportion of ILI among symptomatic case-patients with pandemic (H1N1) 2009 26–42 Literature and unpublished clinical data
C1 (period 2a) Consultation rate among ILI case-patients in secondary and tertiary hospitals 38 Telephone interview conducted by Beijing CDC
C2 (period 2b) Consultation rate among ILI case-patients in secondary and tertiary hospitals 48 Telephone interview conducted by Beijing CDC
D Sampling success rate 80–90 Previous surveillance data
E Sensitivity of test 95–100 Professional recommendations

*ECDC, European Centre for Disease Prevention and Control; ILI, influenza-like illness; Beijing CDC, Beijing Center for Disease Prevention and Control.
†The multiplier model was only used for phase 2 in this study, and phase 2 was divided into 2 periods, period 2a and period 2b. During phase 2, the true number of infections was calculated by multiplying the baseline by the estimation coefficient, using the multiplier model. The baseline case number was equal to the sum of product of weekly ILIs number in level 2/3 hospitals and the corresponding weekly pandemic (H1N1) 2009 positive rate among case-patients with ILIs. The estimation coefficient was obtained by multiplying the reciprocal of the parameters mentioned in this table.
The baseline case numbers in periods 2a and 2b were 6,520 and 171,899, respectively.

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