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American Journal of Epidemiology Advance Access published online on May 21, 2007
American Journal of Epidemiology, doi:10.1093/aje/kwm076
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American Journal of Epidemiology Copyright © 2007 by the Johns Hopkins Bloomberg School of Public Health All rights reserved; printed in U.S.A.

ORIGINAL CONTRIBUTIONS

Pneumococcal Carriage in United Kingdom Families: Estimating Serotype-specific Transmission Parameters from Longitudinal Data

Alessia Melegaro1, Yoon Choi1,2, Richard Pebody2 and Nigel Gay1

1 Modelling and Economics Unit, Centre for Infections, Health Protection Agency, London, United Kingdom
2 Immunisation Department, Centre for Infections, Health Protection Agency, London, United Kingdom

Correspondence to Dr. Alessia Melegaro, Modelling and Economics Unit, Centre for Infections, Health Protection Agency, 61 Colindale Avenue, London NW9 5EQ, United Kingdom (e-mail: alessia.melegaro{at}hpa.org.uk).

Received for publication November 23, 2005. Accepted for publication January 23, 2007.

Repeated observations of pneumococcal infection in 121 United Kingdom families (October 2001–July 2002) were used to explore the transmission properties of five highly prevalent pneumococcal serotypes (6A, 6B, 14, 19F, 23F). A family-based Markov model was developed, and maximum likelihood estimates were produced for model parameters. The authors found higher community acquisition rates among preschool children for all serotypes and higher within-household transmission for 6A and 14. Significant differences in the spontaneous clearance rate were estimated between age categories and serotypes, with 6B being carried for almost 4 months in children. Different mechanisms of competition between serotypes were investigated, and a complete exclusion model (i.e., the resident strain cannot be outcompeted by challengers) was discarded in favor of a competing mechanism that leaves a resident serotype partially or fully susceptible to challengers. Large variation was found in the challenging strength, which was low for 19F and 23F and high for 6A and 6B. Serotype 6B was the only one characterized by high resistance capacity. Only small differences in the transmission characteristics were found when vaccine and nonvaccine serotypes were grouped, suggesting that a serotype-specific analysis is needed to detect distinctive serotype behavior.

disease transmission; longitudinal studies; models, statistical; pneumococcal infections; pneumonia, pneumococcal; Streptococcus pneumoniae


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