Inactivation of avian influenza virus inoculated into ground beef patties cooked on a commercial open-flame gas grill

Authors: Luchansky, John; Porto-Fett, Anna; Suarez, David; Spackman, Erica

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: The global outbreak of bird flu due to avian influenza virus (AIV) has resulted in the loss of some 100 million poultry across 48 U.S. states. Since March of 2024 AIV has also been recovered from dairy cow herds and from raw milk obtained from dairy cattle infected with this virus. In addition, viral genetic material was detected in about 20% of some 300 pasteurized retail milk products, but infectious live virus were not subsequently detected in these same samples. In April of 2024, genetic material from the virus was also detected in 1 of 109 tissue samples tested from condemned cull dairy cows but was not recovered from 30 retail ground beef samples. There have also been at least three cases of bird flu infection that were confirmed in dairy farm workers. Because cull dairy cows comprise about 10% of U.S. beef production, there has been growing concern that if AIV is found in retail ground beef, then would recommended cooking practices be sufficient to inactivate this virus. To find out, we purposefully inoculated ground beef patties (ca. 20% fat) with high levels of a single isolate of AIV and cooked the resulting patties on a gas grill. Cooking inoculated ground beef patties to a rare degree of doneness (about 120°F internal temperature) as measured with a thermometer reduced infectious virus levels by about 300 to 500 fold per gram of patty, whereas cooking patties on a gas grill to a medium degree of doneness (about 145°F internal temperature) or to well done (about 160°F internal temperature; the USDA FSIS recommended minimum internal temperature for ground beef) reduced infectious virus levels at least 500,000 fold per gram of patty (no infectious virus could be detected). Although limited in both scope and in numbers of patties analyzed, our findings suggest that the current risk for humans becoming infected with AIV from a beef source is negligible because proper cooking will eliminate AIV from ground beef patties.

Technical Abstract: With the emergence of clade 2.3.4.4b H5N1 highly pathogenic avian influenza virus (AIV) infection of dairy cattle and its subsequent detection in raw milk, coupled with recent AIV infections affecting dairy farm workers, experiments were conducted to affirm the safety of cooked ground beef related to AIV because such meat is often derived from cull dairy cows. Specifically, retail ground beef (percent lean:fat = ca. 80:20) was inoculated with a single AIV isolate to an initial level of 5.6 log10 EID50 per patty. The inoculated meat was pressed into patties (ca. 2.54 cm thick, ca. 300 g each) and then held at 4°C for up to 60 min. In each of two trials, two patties for each of the following three treatments were cooked on a commercial open-flame gas grill to internal instantaneous temperatures of 48.9°C (120°F), 62.8°C (145°F), or 71.1°C (160°F). Cooking inoculated ground beef patties to 48.9°C resulted in a = 2.5 log10 EID50 reduction in infectious virus per 300 g of ground beef as assessed via quantification of virus in embryonating chicken eggs (ECE). Likewise, cooking patties on a gas grill to 62.8°C or to the USDA FSIS recommended minimum internal temperature for ground beef of 71.1°C resulted in a = 5.6 log10 EID50 reduction in infectious virus per 300 g (i.e., no viable virus could be detected). These data establish that levels of infectious AIV are substantially reduced within inoculated ground beef patties using recommended cooking procedures.