Household transmission of SARS, 2003.
BACKGROUND
In the 2003 outbreak in Toronto (in Ontario, Canada) of severe acute respiratory syndrome (SARS), about 20% of cases resulted from household transmission. The purpose of our study was to determine characteristics associated with the transmission of SARS within households.


METHODS
A retrospective cohort of SARS-affected households was studied to determine risk factors for household transmission. Questionnaires addressed characteristics of the index case, the household and behaviours among household members. Potential risk factors for secondary transmission of infection were assessed in regression models appropriate to the outcome (secondary cases) and nonindependence of household members.


RESULTS
The 74 households that participated included 18 secondary cases and 158 uninfected household members in addition to the 74 index cases. The household secondary attack rate was 10.2% (95% confidence interval [CI] 6.7%-23.5%). There was a linear association between the time the index patient spent at home after symptom onset and the secondary attack rate. Infected health care workers who were index cases had lower rates of household transmission.


CONCLUSIONS
SARS transmission in households is complex and increases with the length of time an ill person spends at home. Risk of transmission was lower when the index case was a health care worker. Rapid case identification is the public health measure most useful in minimizing exposure in the home.
Wilson-Clark
Samantha D
SD
Canadian Field Epidemiology Program, Ottawa Ont. wsamanth@region.waterloo.on.ca
Deeks
Shelley L
SL
Gournis
Effie
E
Hay
Karen
K
Bondy
Susan
S
Kennedy
Erin
E
Johnson
Ian
I
Rea
Elizabeth
E
Kuschak
Theodore
T
Green
Diane
D
Abbas
Zahid
Z
Guarda
Brenda
B
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D018562:Disease Transmission, Infectious; D005191:Family Characteristics; D005192:Family Health; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D009864:Ontario / Q000453:epidemiology; D012189:Retrospective Studies; D012307:Risk Factors; D045169:Severe Acute Respiratory Syndrome / Q000635:transmission*