Case-ascertained study of household transmission of seasonal influenza — South Africa, 2013

Abstract

Summary Objectives 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. Conclusion 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.

Intra-host and intra-household diversity of influenza A viruses during household transmissions in the 2013 season in 2 peri-urban communities of South Africa

“…The study was conducted in two peri-urban sites located in Klerksdorp (Matlosana), North West Province and Pietermaritzburg (Msunduzi), KwaZulu-Natal Province, South Africa. This study was part of a larger study investigating transmission dynamics of seasonal influenza in South African households [ 13 ]. Index cases were identified and consented at primary care clinics when they presented with influenza-like-illness (ILI) (defined as cough and self-reported or measured fever (≥38°C) with onset in the 3 days prior to presentation), between May and October 2013 (South African influenza season).…”

“…Index cases were identified and consented at primary care clinics when they presented with influenza-like-illness (ILI) (defined as cough and self-reported or measured fever (≥38°C) with onset in the 3 days prior to presentation), between May and October 2013 (South African influenza season). In addition each index case had to meet the following criteria: (i) test positive on a rapid influenza diagnostic test (RIDT) at the point of care using the Becton Dickinson (BD) Veritor™ system; and (ii) live with at least 2 household contacts who did not have symptoms suggestive of influenza at the time of enrolment [ 13 ]. Influenza positive RIDT results were confirmed by real-time reverse transcription polymerase chain reaction (rRT-PCR) at the National Institute for Communicable Diseases (NICD), Johannesburg, South Africa.…”

“…A recent case-ascertained household transmission study (HTS) investigated the secondary infection risk, serial interval, and associated risk factors for influenza transmission in household contacts of individuals infected with seasonal influenza in 2 peri-urban communities in South Africa [ 13 ]. The peri-urban communities from which study participants were drawn, Pietermaritzburg and Klerksdorp, consists of mostly single-family houses and informal dwellings, where 50% (n = 15) of households participating in the study reported having 2 or more people share a room for sleeping, previously identified as a risk factor for secondary influenza transmission.…”

“…The peri-urban communities from which study participants were drawn, Pietermaritzburg and Klerksdorp, consists of mostly single-family houses and informal dwellings, where 50% (n = 15) of households participating in the study reported having 2 or more people share a room for sleeping, previously identified as a risk factor for secondary influenza transmission. This study reported a secondary infection risk of 19% and a mean serial interval of 2.1 days [ 13 ].…”

Household Transmission of Influenza Virus

“…We conducted a review of household transmission studies of influenza, explored the typical design and implementation of these studies, and contrasted and compared their major findings. We identified 56 relevant published studies (see Tables S1 and S2 in the supplemental information online) 34 , 35 , 38 , 40 , 42 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 . In the following sections, we describe the key design features of transmission studies and summarize the scientific findings of these studies in terms of the basic transmissibility of influenza viruses in households, the factors affecting transmission, and the effectiveness of specific control measures in household settings.…”