Subclinical Avian Influenza A(H5N1) Virus Infection in Human, Vietnam

Mai Quynh Le

, Peter Horby, Annette Fox, Hien Tran Nguyen, Hang Khanh Le Nguyen, Phuong Mai Vu Hoang, Khanh Cong Nguyen, Menno D. de Jong, Rienk E. Jeeninga, H. Rogier van Doorn, Jeremy Farrar, and Heiman F.L. Wertheim

Author affiliations: National Institute of Hygiene and Epidemiology, Hanoi, Vietnam (M.Q.Le, H.T. Nguyen, H.K.L. Nguyen, P.M.V. Hoang, K.C. Nguyen); Wellcome Trust Major Overseas Programme, Hanoi and Ho Chi Minh City, Vietnam (P. Horby, A. Fox, M.D. de Jong, H.R. van Doorn, J. Farrar, H.F.L. Wertheim); Centre for Tropical Medicine, Oxford, United Kingdom (P. Horby, A. Fox, H.R. van Doorn, J. Farrar, H.F.L. Wertheim); Academic Medical Center, Amsterdam, the Netherlands (M.D. de Jong, R.E. Jeeninga)

Abstract

Laboratory-confirmed cases of subclinical infection with avian influenza A(H5N1) virus in humans are rare, and the true number of these cases is unknown. We describe the identification of a laboratory-confirmed subclinical case in a woman during an influenza A(H5N1) contact investigation in northern Vietnam.

In 2012, a debate was published in Science about the number of humans who have experienced subclinical infection with avian influenza A H5 and how this unknown denominator could affect the case-fatality rate reported by the World Health Organization (1,2). The controversy rests, to a large extent, on interpretation of serologic tests used to detect prior H5 infection and the paucity of virologically confirmed subclinical or mild cases. Here we describe a case of subclinical avian influenza A H5 infection, confirmed both virologically and serologically.

The Case

The subclinical case was detected in 2011 during a contact investigation of a 40-year-old man suspected of having influenza A(H5N1) virus infection. The man’s household had sick poultry that were consumed by household members. The chickens roamed close to the sleeping area of the household members. The index case-patient, his daughter, and his daughter-in-law were involved in slaughtering and preparing the chickens. The index case-patient had fever, cough, dyspnea, and diarrhea that progressed over 2 days, leading to hospital admission. Despite intensive care and treatment with oseltamivir and antibiotics, the disease progressed, and he died 2 days later.