Reconstructing the household transmission of influenza in the suburbs of Tokyo based on clinical cases

Abstract

Background Influenza is a public health issue that needs to be addressed strategically. The assessment of detailed infectious profiles is an important part of this effort. Household transmission data play a key role in estimating such profiles. We used diagnostic and questionnaire-based data on influenza patients at a Japanese clinic to estimate the detailed infectious period (as well as incubation period, symptomatic and infectious periods, and extended infectious period after recovery) and the secondary attack ratio (SAR) of influenza for households of various sizes based on a modified Cauchemez-type model. Results The data were from enrolled patients with confirmed influenza who were treated at the Hirotsu Clinic (Kawasaki, Japan) with a neuraminidase inhibitor (NAI) during six northern hemisphere influenza seasons between 2010 and 2016. A total of 2342 outpatients, representing 1807 households, were included. For influenza type A, the average incubation period was 1.43 days (95% probability interval, 0.03–5.32 days). The estimated average symptomatic and infective period was 1.76 days (0.33–4.62 days); the extended infective period after recovery was 0.25 days. The estimated SAR rose from 20 to 32% as household size increased from 3 to 5. For influenza type B, the average incubation period, average symptomatic and infective period, and extended infective period were estimated as 1.66 days (0.21–4.61), 2.62 days (0.54–5.75) and 1.00 days, respectively. The SAR increased from 12 to 21% as household size increased from 3 to 5. Conclusion All estimated periods of influenza type B were longer than the corresponding periods for type A. However, the SAR for type B was less than that for type A. These results may reflect Japanese demographics and treatment policy. Understanding the infectious profiles of influenza is necessary for assessing public health measures.

Comparison of Intra-Familial Transmission of Influenza Virus From Index Patients Treated With Baloxavir Marboxil or Oseltamivir Using an Influenza Transmission Model and a Health Insurance Claims Database

“…Saito et al (2021) [ 19 ] described a natural course of influenza infection using an agent-based model that divides the period from the first influenza infection to the disappearance of infectivity into four distinct periods ( Figure 1 ). We introduced a distribution for the variation in each period for data on infection within families and a method for maximum likelihood estimation of the parameters of each distribution, providing distributions for a , c , and d under the assumption that the disease develops at the point of infectivity, that is, b = 0.…”

“… Modified model of agent-based intra-familial transmission of influenza. Parameters a and b are based on the results by Saito et al [ 19 ], whereas parameters c and d are based on the results by Hayden et al [7]. The beginning of period c is available from JMDC-DB as the date of a positive rapid influenza diagnostic test in most cases.…”

“…Scenario 2, secondary infection from external sources. Left panel describes the treatment course of influenza infection as described by Saito et al [ 19 ], whereas the right panel describes how intra-familial infections were defined in JMDC-DB. Abbreviation: JMDC-DB, JMDC Claims Database.…”

“…Based on the results of the CAPSTONE-1 RCT [ 7 ] and the pediatric open-label study on BXM [ 8 ], we assumed that there is no significant difference in the duration of viral shedding between children and adults. If a family member other than the IC had a diagnosis of influenza infection, we estimated the date of influenza infection for that family member by generating a random number corresponding to periods a-b that follows a gamma distribution (shape parameter, 0.99; scale parameter, 1.46) with a mean of 1.43 days, as described by Saito et al [ 19 ]. Consequently, we defined the presence of intra-familial infection when the duration of influenza virus infectivity (shedding period) for each anti-influenza agent in IC (periods b – d ) overlapped with the virus incubation period of other family members infected with influenza (periods a – b ).…”

“…We applied the previously described influenza intra-familial infection model [ 19 ] and the viral shedding period of BXM and OTV described in a clinical study [ 7 ] to the data set previously analyzed by Komeda et al [ 18 ]. This enabled simulation of the duration of influenza virus infection for both anti-influenza agents in ICs and the incubation period of influenza virus (a period when a person is infected but does not show symptoms) in other family members infected with influenza, thereby overcoming the limitation of the previously published studies.…”