Secondary household transmission of 2009 pandemic influenza A (H1N1) virus among an urban and rural population in Kenya, 2009-2010.
BACKGROUND
In Kenya, >1,200 laboratory-confirmed 2009 pandemic influenza A (H1N1) (pH1N1) cases occurred since June 2009. We used population-based infectious disease surveillance (PBIDS) data to assess household transmission of pH1N1 in urban Nairobi (Kibera) and rural Lwak.


METHODS
We defined a pH1N1 patient as laboratory-confirmed pH1N1 infection among PBIDS participants during August 1, 2009-February 5, 2010, in Kibera, or August 1, 2009-January 20, 2010, in Lwak, and a case household as a household with a laboratory-confirmed pH1N1 patient. Community interviewers visited PBIDS-participating households to inquire about illnesses among household members. We randomly selected 4 comparison households per case household matched by number of children aged <5. Comparison households had a household visit 10 days before or after the matched patient symptom onset date. We defined influenza-like illnesses (ILI) as self-reported cough or sore throat, and a self-reported fever ≤8 days after the pH1N1 patient's symptom onset in case households and ≤8 days before selected household visit in comparison households. We used the Cochran-Mantel-Haenszel test to compare proportions of ILIs among case and comparison households, and log binomial-model to compare that of Kibera and Lwak.


RESULTS
Among household contacts of patients with confirmed pH1N1 in Kibera, 4.6% had ILI compared with 8.2% in Lwak (risk ratio [RR], 0.5; 95% confidence interval [CI], 0.3-0.9). Household contacts of patients were more likely to have ILIs than comparison-household members in both Kibera (RR, 1.8; 95% CI, 1.1-2.8) and Lwak (RR, 2.6; 95% CI, 1.6-4.3). Overall, ILI was not associated with patient age. However, ILI rates among household contacts were higher among children aged <5 years than persons aged ≥5 years in Lwak, but not Kibera.


CONCLUSIONS
Substantial pH1N1 household transmission occurred in urban and rural Kenya. Household transmission rates were higher in the rural area.
Epidemic Intelligence Service, Office of Workforce and Career Development, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America. clara_kim@alumni.upenn.edu
Clara Y
CY
Kim
Robert F
RF
Breiman
Leonard
L
Cosmas
Allan
A
Audi
Barrack
B
Aura
Godfrey
G
Bigogo
Henry
H
Njuguna
Emmaculate
E
Lebo
Lilian
L
Waiboci
M Kariuki
MK
Njenga
Daniel R
DR
Feikin
Mark A
MA
Katz
D005191:Family Characteristics; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission*; D007630:Kenya / Q000453:epidemiology; D015233:Models, Statistical; D016017:Odds Ratio; D058873:Pandemics / Q000706:statistics & numerical data*; D011159:Population Surveillance; D012424:Rural Population; D014505:Urban Population