Pandemic H1N1 virus transmission and shedding dynamics in index case households of a prospective Vietnamese cohort

Abstract

SummaryObjectivesInfluenza 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.MethodsHealth-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.ResultsIndex 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).ConclusionsIn 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.

Review Article

“…Studies in the group of outbreak/epidemic investigations included eight household transmission studies (20–27) and three studies in other settings (28–30). In these studies, identification of initial laboratory-confirmed cases was followed by intense follow-up of exposed persons that included repeated collection of respiratory specimens or sera regardless of symptomatic illness.…”

Influenza A Virus Shedding and Infectivity in Households

“…This indicates that the duration of virus shedding detectable by PCR may be longer than the infectious period. It may also indicate that other factors, such as the severity of symptoms [28] or social behavior [29], influence infectivity within households. One caveat of this analysis is that our study design permitted households to be enrolled within 2 days of illness onset in the index case patients, whereas households with multiple index case patients were excluded.…”

“…We found that all the models we considered that used viral loads to approximate infectivity of a case imperfectly explained the timing of influenza secondary infections in households, with the best-fitting models-V γ , log V, and (log V ) γ -still overestimating transmission >3 days after symptom onset. This may be because other factors, such as the severity of symptoms [28] or social behavior [29], may also influence infectivity within households. Identification of more accurate correlates of infectivity will be important to inform control policies and disease modeling.…”

Study of the Epidemiological Features and Clinical Manifestations of the Preceding Epidemic of Influenza A (H1N1) as a Guide for Dealing With the 2015 Outbreak in the Qazvin Province, Iran

“…In an experimental study using laboratory animals, the release of respiratory droplets was confirmed as the principal route of transmission (11). In a human study carried out in south Asia, wet cough was shown to act as an important risk factor for transmission of H1N1-2009 virus from index cases to household contacts (OR: 1.56, CI: 1.22-1.99) (12). In a consultation meeting held in the Eastern Mediterranean region, large particle droplets were introduced as the main route of transmission of the virus (13).…”