Modeling Transmission of Human Metapneumovirus in a Long-Term Care Facility

Abstract

Background: In September 2019, the Louisiana Department of Health (LDH) was notified of a possible outbreak of influenza in a nursing home. Upon investigation, the infectious agent was determined to be human metapneumovirus (HMPV). By the conclusion of the outbreak, 35 (31.3%) symptomatic cases were identified of which 15 were laboratory-confirmed HMPV. Public health coordination, infection control interventions, environmental cleaning audits, halting new admissions, and ceasing group activities are credited with stopping transmission. Considering the high attack rate, LDH epidemiologists examined scenarios wherein the aforementioned interventions were not utilized. The aim of this analysis is to describe transmission of HMPV in a 112-bed nursing home using mathematical models under conditions wherein interventions were not readily implemented. Methods: Two deterministic and 1 stochastic susceptible–preinfectious–infectious–recovered (SEIR) models are presented. Although recovered persons can be susceptible to HMPV following an infection experience, the potential for reinfection was not considered for this analysis. Fixed variables considered include a 5-day incubation period, basic reproduction number of 2, 14-day infectious period, and 112 susceptible patients. Three counterfactual modeling conditions are considered: delaying notification of an outbreak to public health epidemiologists (model 1), staff hand hygiene compliance of 50% (model 2), and continuing to accept new admissions (model 3). Average rate of recovery per day was and other metrics are used to demonstrate the number of susceptible individuals. Excel workbooks developed by Vynnycky and White (2010) were used for analysis. Results: In model 1, the average rate of onset of infectiousness per day = 0.20, and the average recovery rate per day = 0.07. With no notification to public health epidemiologists, all 112 patients would have been infected with HMPV after 94 days. The reproductive number was doubled to 4 in model 2 to posit poor healthcare worker hand hygiene of 50% compliance. Given this, the number of days until all patients are infected with HMPV decreases to 39 days. Finally, the stochastic scenario (model 3) demonstrates that the number of newly infected persons per day = 0.86, and the hazard rate for infectious individuals becoming immune = 0.07. Conclusions: Infection control interventions are extremely useful for containing viral respiratory diseases for which there is no vaccine or treatment. Mathematical models can communicate utility of public health interventions in the presence of outbreaks. These models demonstrate worst-case scenarios for infection spread.

Funding: None

Disclosures: None