title: Case-ascertained study of household transmission of seasonal influenza - South Africa, 2013.
abstract: OBJECTIVE
  The household is important in influenza transmission due to intensity of contact. Previous studies reported secondary attack rates (SAR) of 4-10% for laboratory-confirmed influenza in the household. Few have been conducted in middle-income countries.
  
  
  METHODS
  We performed a case-ascertained household transmission study during May-October 2013. Index cases were patients with influenza-like-illness (cough and self-reported or measured fever (≥38 °C)) with onset in the last 3 days and no sick household contacts, at clinics in South Africa. Household contacts of index cases with laboratory-confirmed influenza were followed for 12 days.
  
  
  RESULTS
  Thirty index cases in 30 households and 107/110 (97%) eligible household contacts were enrolled. Assuming those not enrolled were influenza negative, 21/110 household contacts had laboratory-confirmed influenza (SAR 19%); the mean serial interval was 2.1 days (SD = 0.35, range 2-3 days). Most (62/82; 76%) household contacts who completed the risk factor questionnaire never avoided contact and 43/82 (52%) continued to share a bed with the index case after illness onset.
  
  
  CONCLUSIONS
  SAR for laboratory-confirmed influenza in South Africa was higher than previously reported SARs. Household contacts did not report changing behaviors to prevent transmission. These results can be used to understand and predict influenza transmission in similar middle-income settings.
authors.affiliation: Epidemic Intelligence Service, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, USA; Global Disease Detection Branch, Division of Global Health Protection, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, USA; US Public Health Service, 5600 Fishers Ln, Rockville, MD, USA. Electronic address: piyengar@gmail.com.
authors.forename: Preetha
authors.initials: P
authors.lastname: Iyengar
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, 1 Modderfontein Rd, Sandringham, Johannesburg, South Africa; School of Public Health, Faculty of Health Science, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg, South Africa.
authors.forename: Claire
authors.initials: C
authors.lastname: von Mollendorf
authors.affiliation: Influenza Program, Centers for Disease Control and Prevention-South Africa, PO Box 9536, Pretoria, South Africa; Influenza Division, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, USA.
authors.forename: Stefano
authors.initials: S
authors.lastname: Tempia
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, 1 Modderfontein Rd, Sandringham, Johannesburg, South Africa.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Moerdyk
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, 1 Modderfontein Rd, Sandringham, Johannesburg, South Africa.
authors.forename: Ziyaad
authors.initials: Z
authors.lastname: Valley-Omar
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, 1 Modderfontein Rd, Sandringham, Johannesburg, South Africa.
authors.forename: Orienka
authors.initials: O
authors.lastname: Hellferscee
authors.affiliation: Perinatal HIV Research Unit, University of the Witwatersrand, Johns Hopkins University Center for TB Research, 1550 Orleans Street, Baltimore, MD, USA.
authors.forename: Neil
authors.initials: N
authors.lastname: Martinson
authors.affiliation: Department of Pediatrics, University of KwaZulu-Natal, King George V Ave, Glenwood, Durban, South Africa.
authors.forename: Meera
authors.initials: M
authors.lastname: Chhagan
authors.affiliation: US Public Health Service, 5600 Fishers Ln, Rockville, MD, USA; Influenza Division, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, USA.
authors.forename: Meredith
authors.initials: M
authors.lastname: McMorrow
authors.affiliation: Modeling Unit, National Center for Immunization and Respiratory Disease, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, USA; Epidemiological Modelling Unit, Department of Epidemiology and Preventive Medicine, Monash University, 99 Commercial Road, Melbourne, Australia.
authors.forename: Manoj
authors.initials: M
authors.lastname: Gambhir
authors.affiliation: Mathematical Modelling of Infectious Diseases Unit, Institut Pasteur, 28 rue du Docteur Roux, Paris, France.
authors.forename: Simon
authors.initials: S
authors.lastname: Cauchemez
authors.affiliation: Department of Medicine, Klerksdorp Tshepong Hospital Complex and University of the Witwatersrand, Corner of OR Tambo and John Orr Street, Klerksdorp, South Africa.
authors.forename: Ebrahim
authors.initials: E
authors.lastname: Variava
authors.affiliation: Perinatal HIV Research Unit, University of the Witwatersrand, Johns Hopkins University Center for TB Research, 1550 Orleans Street, Baltimore, MD, USA.
authors.forename: Katlego
authors.initials: K
authors.lastname: Masonoke
authors.affiliation: US Public Health Service, 5600 Fishers Ln, Rockville, MD, USA; Influenza Program, Centers for Disease Control and Prevention-South Africa, PO Box 9536, Pretoria, South Africa; Influenza Division, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, USA.
authors.forename: Adam L
authors.initials: AL
authors.lastname: Cohen
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, 1 Modderfontein Rd, Sandringham, Johannesburg, South Africa; School of Public Health, Faculty of Health Science, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg, South Africa. Electronic address: cherylc@nicd.ac.za.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Cohen
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005191:Family Characteristics; D005192:Family Health; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification / Q000502:physiology; D053122:Influenza A Virus, H3N2 Subtype / Q000302:isolation & purification / Q000502:physiology; D007251:Influenza, Human / Q000453:epidemiology / Q000635:transmission* / Q000821:virology*; D008297:Male; D012307:Risk Factors; D012621:Seasons; D013019:South Africa / Q000453:epidemiology; D011795:Surveys and Questionnaires; D055815:Young Adult
keywords: Household transmission; Influenza; Secondary infection risk; Serial interval; South Africa