Frequent Asymptomatic Respiratory Syncytial Virus Infections During an Epidemic in a Rural Kenyan Household Cohort.
BACKGROUND
The characteristics, determinants, and potential contribution to transmission of asymptomatic cases of respiratory syncytial virus (RSV) infection have not been well described.


METHODS
A cohort of 47 households (493 individuals) in coastal Kenya was recruited and followed for a 26-week period spanning a complete RSV season. Nasopharyngeal swab specimens were requested weekly, during the first 4 weeks, and twice weekly thereafter from all household members, regardless of illness status. The samples were screened for a range of respiratory viruses by multiplex real-time polymerase chain reaction.


RESULTS
Tests on 16,928 samples yielded 205 RSV infection episodes in 179 individuals (37.1%) from 40 different households. Eighty-six episodes (42.0%) were asymptomatic. Factors independently associated with an increased risk of asymptomatic RSV infection episodes were higher age, shorter duration of infection, bigger household size, lower peak viral load, absence of concurrent RSV infections within the household, infection by RSV group B, and no prior human rhinovirus infections. The propensity of RSV spread in households was dependent on symptom status and amount (duration and load) of virus shed.


CONCLUSIONS
While asymptomatic RSV was less likely to spread, the high frequency of symptomless RSV infection episodes highlights a potentially important role of asymptomatic infections in the community transmission of RSV.
Epidemiology and Demography Department, KEMRI-Wellcome Trust Research Programme, Centre for Geographic Medicine Research-Coast, Kilifi, Kenya.
Patrick K
PK
Munywoki
Epidemiology and Demography Department, KEMRI-Wellcome Trust Research Programme, Centre for Geographic Medicine Research-Coast, Kilifi, Kenya.
Dorothy C
DC
Koech
Epidemiology and Demography Department, KEMRI-Wellcome Trust Research Programme, Centre for Geographic Medicine Research-Coast, Kilifi, Kenya.
Charles N
CN
Agoti
Epidemiology and Demography Department, KEMRI-Wellcome Trust Research Programme, Centre for Geographic Medicine Research-Coast, Kilifi, Kenya.
Ann
A
Bett
High Containment Microbiology, Public Health England, Salisbury.
Patricia A
PA
Cane
London School of Hygiene and Tropical Medicine (WIDER) Centre, University of Warwick, Coventry, United Kingdom.
Graham F
GF
Medley
Epidemiology and Demography Department, KEMRI-Wellcome Trust Research Programme, Centre for Geographic Medicine Research-Coast, Kilifi, Kenya School of Life Sciences (WIDER) Centre, University of Warwick, Coventry, United Kingdom Warwick Infectious Disease Epidemiology Research (WIDER) Centre, University of Warwick, Coventry, United Kingdom.
D James
DJ
Nokes
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D058345:Asymptomatic Infections / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D058872:Epidemics / Q000706:statistics & numerical data*; D005191:Family Characteristics; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007630:Kenya / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D018357:Respiratory Syncytial Virus Infections / Q000453:epidemiology*; D012424:Rural Population / Q000706:statistics & numerical data; D055815:Young Adult
Kenya; asymptomatic; households; respiratory syncytial virus (RSV); transmission