Results from a test-and-treat study for influenza among residents of homeless shelters in King County, WA: A stepped-wedge cluster-randomized trial

Abstract

Background: Persons experiencing homelessness face increased risk of influenza as overcrowding in congregate shelters can facilitate influenza virus spread. Data regarding on-site influenza testing and antiviral treatment within homeless shelters remain limited.

Methods: We conducted a cluster-randomized stepped-wedge trial of point-of-care molecular influenza testing coupled with antiviral treatment with baloxavir or oseltamivir in residents of 14 homeless shelters in Seattle, WA, USA. Residents ≥3 months with cough or ≥2 acute respiratory illness (ARI) symptoms and onset <7 days were eligible. In control periods, mid-nasal swabs were tested for influenza by reverse transcription polymerase chain reaction (RT-PCR). The intervention period included on-site rapid molecular influenza testing and antiviral treatment for influenza-positives if symptom onset was <48 h. The primary endpoint was monthly influenza virus infections in the control versus intervention periods. Influenza whole genome sequencing was performed to assess transmission and antiviral resistance.

Results: During 11/15/2019-4/30/2020 and 11/2/2020-4/30/2021, 1283 ARI encounters from 668 participants were observed. Influenza virus was detected in 51 (4%) specimens using RT-PCR (A = 14; B = 37); 21 influenza virus infections were detected from 269 (8%) intervention-eligible encounters by rapid molecular testing and received antiviral treatment. Thirty-seven percent of ARI-participant encounters reported symptom onset < 48 h. The intervention had no effect on influenza virus transmission (adjusted relative risk 1.73, 95% confidence interval [CI] 0.50-6.00). Of 23 influenza genomes, 86% of A(H1N1)pdm09 and 81% of B/Victoria sequences were closely related.

Conclusion: Our findings suggest feasibility of influenza test-and-treat strategies in shelters. Additional studies would help discern an intervention effect during periods of increased influenza activity.

Keywords: antiviral treatment; homeless shelters; influenza; randomized control trial; rapid molecular influenza test.

FIGURE 1

Stepped‐wedge cluster‐randomized trial design and shelter randomization assignments, Years 1 and 2. COVID‐19, coronavirus disease 2019; RCT, randomized controlled trial

FIGURE 2

(A) Study design overview including participant‐level study flow of the test‐and‐treat strategy from 11/15/19 to 4/30/21. (B) Total number of participants completing intervention study procedure steps based on eligibility screening. ARI, acute respiratory illness; RT‐PCT, reverse transcription polymerase chain reaction

FIGURE 3

Maximum likelihood phylogenetic trees for (A) influenza A and (B) influenza B. Trees include all sequenced study samples and all genomes for samples collected in Washington (WA) during the study timeframe that have been deposited in GISAID.