Estimation of the incubation period for pandemic influenza during 1918–19

Abstract number: 1733_547

Nishiura H.

Background: The incubation period of influenza has not been precisely understood and is yet to be clarified.

Methods: This study reassessed an epidemiologic record of pandemic influenza observed on the ocean during voyages. The original data is based on observations of 92 voyages from 1918–19, departing from several ports in Australia with incubating individuals. Although infection event is not directly observable, the incidence (i.e., time of onset) is recorded according to the date after departure. Whereas Dr. Anderson Gray McKendrick (1876–1943) previously used a daily probability of onset to infer the incubation period, I show how to interpret the data and improve the estimation method assuming lognormal distribution for the incubation period.

Results: Maximum likelihood estimates of the mean incubation period and coefficient of variation were 1.34 days and 53.1%, respectively. The estimate was roughly consistent with the suggestion of Dr. McKendrick proposing 32.71 hours as the mean. An explicit distribution of the incubation period was obtained. Dr. McKendrick's method appeared to have assumed the complementary cumulative distribution function for the observed data.

Conclusions: Although it is often difficult to determine the incubation period without explicit information of the time of exposure, a hint to limit most probable time of exposure enables the estimation. Whereas the precision might be still limited, the length and variance of the incubation period would be directly relevant to public health interventions (i.e., determination of the time to quarantine exposed individuals).

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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