Development of methods for the recovery and disinfection of human enteric viruses and other microbes on produce

Methods were developed for the recovery and disinfection of human enteric viruses and other microbes on fruits and vegetables (produce). Seeded viruses and other microbes were recovered from produce using specifically formulated eluents, some of which were compatible with both infectivity and nucleic acid detection methods. Between 100–1000 infectious units of hepatitis A virus (HAV) and poliovirus (PV) were routinely detectable from a single produce sample using surface elution, and with simple modifications, existing methods detected about 1–10 infectious units of Escherichia coli B, coliphage MS2, and Salmonella typhimurium on produce. Low levels of wild-type HAV, hepatitis E virus, and Norwalk virus from diluted feces were detectable in produce eluates using the reverse-transcription polymerase chain reaction (RT-PCR). Soil, fecal material, and extraneous plant material interfered with RT-PCR and cell infectivity methods for virus detection, but this was overcome by more extensive processing. The effectiveness of chemical sanitizers to inactivate HAV and other microbes on produce was determined using the developed recovery methods. When produce items were exposed to water containing 10–20 mg/L of free chlorine for up to 5 minutes, infectious HAV and E. coli were inactivated by about 90–99%, with more rapid and extensive inactivation at higher chlorine concentrations and longer contact times. Exposure of produce to water containing as much as 80 mg/L peroxyacetic acid (POAA) had no effect on HAV but was effective for the inactivation of E. coli B. Infectious viruses (coliphage MS2) and bacteria on strawberries and tomatoes were reduced by washing with chlorinated water using actual commercial-scale equipment. Overall, bench and field produce disinfection experiments demonstrated that disinfectant-containing water can dramatically reduce the levels of infectious microorganisms on produce, thereby reducing exposure risks from produceborne viruses and bacteria.