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The recent outbreak of highly pathogenic avian influenza (HPAI) in dairy cows has created public health concerns about the potential of consumers being exposed to live virus from commercial dairy products. Previous studies support that pasteurization effectively inactivates avian influenza in milk and an earlier retail milk survey showed viral RNA, but no live virus could be detected in the dairy products tested. Because of the variety of products and processing methods in which milk is used, additional product testing was conducted to determine if HPAI viral RNA could be detected in retail dairy samples, and for positive samples by quantitative real-time RT-PCR (qRT-PCR) further testing for the presence of live virus. Revised protocols were developed to extract RNA from solid dairy products including cheese and butter. The solid dairy product was mechanically liquified with garnet and zirconium beads in a bead beater diluted 1–4 with BHI media. This preprocessing step was suitable in allowing efficient RNA extraction with standard methods. Trial studies were conducted with different cheese types with spiked-in avian influenza virus to show that inoculation of the liquified cheese into embryonating chicken eggs was not toxic to the embryos and allowed virus replication. A total of 167 retail dairy samples, including a variety of cheeses, butter, ice cream, and fluid milk were collected as part of a nationwide survey. A total of 17.4% (29/167) of the samples had detectable viral RNA by qRT-PCR targeting the matrix gene, but all PCR-positive samples were negative for live virus after testing with embryonating egg inoculation. The viral RNA was also evaluated by sequencing part of the hemagglutinin gene using a revised protocol optimized to deal with the fragmented viral RNA. The sequence analysis showed all viral RNA-positive samples were highly similar to previously reported HPAI dairy cow isolates. Using the revised protocols, it was determined that HPAI viral RNA could be detected in a variety of dairy products, but existing pasteurization methods effectively inactivate the virus assuring consumer safety.

Raw (unpasteurized) milk is available for sale and direct human consumption within some states in the United States (US); it cannot be sold or distributed in interstate commerce. Raw milk may contain pathogenic microorganisms that, when consumed, may cause illness and sometimes may result in death. No comprehensive review for prevalence and levels of the major bacterial pathogens in raw milk in the US exists. The objective of the present research was to systematically review the scientific literature published from 2000 to 2019 to estimate the prevalence and levels of Listeria monocytogenes, Salmonella spp., Shiga toxin-producing Escherichia coli (STEC), and Campylobacter spp. in raw milk in the US. Peer-reviewed studies were retrieved systematically from PubMed®, Embase®, and Web of ScienceTM. The unique complete nonduplicate references were uploaded into the Health Assessment Work Collaborative (HAWC). Based on the selection criteria, twenty studies were included in the systematic review and meta-analysis. Comprehensive Meta-Analysis (CMA) was used for statistical analyses, specifically, random effects meta-analyses were used to synthesize raw bulk tank milk (BTM) and milk filters (MF) data. Data from studies using culture and non–culture-based detection methods were included. Forest plots generated in CMA (Biostat, Englewood, NJ) were used to visualize the results. The average prevalence (event rate) of L. monocytogenes, Salmonella spp., STEC, and Campylobacter spp. in raw BTM in the US was estimated at 4.3% (95% confidence intervals [CIs], 2.8–6.5%), 3.6% (95% CIs, 2.0–6.2%), 4.3% (95% CIs, 2.4–7.4%), and 6.0% (95% CIs, 3.2–10.9%), respectively. Estimated prevalence was generally larger in MF than in BTM. There was not enough data to perform a meta-analysis for the prevalence or levels of pathogens in raw milk from retail establishments or other milk categories.