Time course and epidemiological features of COVID-19 resurgence due to cold-chain food or packaging contamination.

Contaminations in frozen food imported from countries with ongoing COVID-19 epidemics have been reported in China. However, the epidemiological features of the outbreaks initiated by material-to-human transmission were less reported. The risk of this route of transmission remains unclear, and strategies to prevent resurgence could be flawed. We aimed to demonstrate the existence of cold-chain food or packaging contamination transmission and describe the time course and epidemiological features associated with the transmission in China. This review was based on the official reports or literature for resurging COVID-19 events that were related to cold-chain food or packaging contamination in China and other countries. Although SARS-CoV-2 on the material surface is not the main source of infection, the closed and humid environment for food packaging and transportation is a place favoring the material-to-human spread of SARS-CoV-2. In this transmission mode, patient zero is often hidden and difficult to detect, such that the outbreak usually can only be perceived after a period of a secret epidemic. Regular testing for high-risk populations and imported cold-chain products, proper disinfection of imported products, and protection of susceptible population while working remain an effective way to detect and prevent SARS-CoV-2 spread.