Pandemic H1N1 virus transmission and shedding dynamics in index case households of a prospective Vietnamese cohort.
OBJECTIVE
Influenza household transmission studies are required to guide prevention strategies but most passively recruit index cases that seek healthcare. We investigated A(H1N1)pdm09 transmission in a household-based cohort during 2009.


METHODS
Health-workers visited 270 households weekly, and collected swabs from influenza-like-illness cases. If A(H1N1)pdm09 was RT-PCR-confirmed, all household members had symptoms assessed and swabs collected daily for 10-15 days. Viral RNA was quantified and sequenced and serology performed on pre-pandemic sera.


RESULTS
Index cases were detected in 20 households containing 81 people. 98.5% lacked A(H1N1)pdm09 neutralizing antibodies in pre-pandemic sera. Eleven (18.6%, 95% CI 10.7-30.4%) of 59 contacts were infected. Virus genetic diversity within households was negligible and less than between households. Index and secondary cases were distributed between mothers, daughters and sons, and had similar virus-RNA shedding and symptom dynamics. Fathers were rarely infected. Five secondary cases (45%) had no apparent symptoms and three shed virus before symptoms. Secondary infection was associated with index case wet cough (OR 1.56, 95% CI 1.22-1.99).


CONCLUSIONS
In this cohort of A(H1N1)pdm09 susceptible persons, virus sequencing was capable of discriminating household from community transmission. Household transmission involved mothers and children but rarely fathers. Asymptomatic or pre-symptomatic shedding was common.
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
Pham Quang
PQ
Thai
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
Le Quynh
le Q
Mai
Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Matthijs R A
MR
Welkers
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
Nguyen Le Khanh
Nle K
Hang
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
Le Thi
le T
Thanh
Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam.
Vu Tien Viet
VT
Dung
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
Nguyen Thi Thu
NT
Yen
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
Tran Nhu
TN
Duong
Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam.
Le Nguyen Minh
le NM
Hoa
Ha Nam Centre for Preventive Medicine, Ha Nam, Viet Nam.
Dang Dinh
DD
Thoang
Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam.
Hoang Thi Huyen
HT
Trang
Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Menno D
MD
de Jong
Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam; Center for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
Heiman
H
Wertheim
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
Nguyen Tran
NT
Hien
Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam; Center for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
Peter
P
Horby
Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam; Center for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK; Department of Microbiology and Immunology, University of Melbourne, Australia. Electronic address: afox@oucru.org.
Annette
A
Fox
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000914:Antibodies, Viral / Q000097:blood; D044466:Asian People; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005191:Family Characteristics; D005260:Female; D014644:Genetic Variation; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000635:transmission* / Q000821:virology*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012367:RNA, Viral / Q000235:genetics; D017422:Sequence Analysis, DNA; D019562:Viral Load; D017201:Virus Shedding; D055815:Young Adult
D000914:Antibodies, Viral; D012367:RNA, Viral
Antibody; Household; Index; Influenza; Pandemic; Secondary; Serial interval; Shedding; Symptoms; Transmission