Epidemiology and Infection

Short Report


Pre-symptomatic transmission of pandemic influenza H1N1 2009: investigation of a family cluster, Brazil

F. T. M. FREITASa1 c1, A. P. S. CABRALa1, E. N. C. BARROSa1, M. J. O. BURIGOa2, R. D. PROCHNOWa2, L. A. SILVAa2, M. A. WIDDOWSONa3 and J. SOBELa3

a1 Secretariat of Health Surveillance, Brazilian Ministry of Health, Brasilia, Brazil

a2 Secretariat of Health of Santa Catarina State, Florianopolis, Brazil

a3 Centers for Disease Control and Prevention, Atlanta, GA, USA


We investigated the first cluster of pandemic influenza H1N1 2009 reported in Brazil in May 2009. The index case-patient had travelled from the USA and had contact with 11 relatives before she presented with symptoms. We conducted face-to-face or telephone interviews with the index case-patient and all suspect cases. We found evidence of pre-symptomatic transmission of the virus to four of her contacts. This finding has public health implications because it indicates that viral transmission in communities may not be prevented solely by isolating symptomatic case-patients.

(Received February 10 2012)

(Revised June 08 2012)

(Accepted June 10 2012)

(Online publication July 16 2012)

Key words

  • Brazil;
  • disease outbreaks;
  • influenza


c1 Author for correspondence: F. T. M. Freitas, Secretaria de Vigilância em Saúde, Ministério da Saúde, Setor Comercial Sul, Quadra 4, Bloco A, 2° andar,70304-000, Brasilia, Brazil. (Email: felipetmf@gmail.com)