In a May 10 update, FDA confirmed that all 297 samples from FDA’s national survey of retail dairy products were found to be negative for viable highly pathogenic H5N1 avian influenza (H5N1 HPAI) virus. On May 20, for continued transparency, FDA provided additional information on our retail sample survey.
Source: Food and Drug Administration
The U.S. Department of Agriculture (USDA), the U.S. Food and Drug Administration (FDA), and the Centers for Disease Control and Prevention (CDC), along with state partners, continue to investigate an outbreak of highly pathogenic avian influenza (HPAI) virus impacting dairy cows in multiple states. Infection with the virus is causing decreased lactation, low appetite, and other symptoms in affected cattle.
The FDA and USDA have indicated that based on the information currently available, our commercial milk supply is safe because of these two reasons:
1) the pasteurization process and
2) the diversion or destruction of milk from sick cows.
The pasteurization process has served public health well for more than 100 years. Pasteurization is a process that kills harmful bacteria and viruses by heating milk to a specific temperature for a set period of time to make milk safer. Even if virus is detected in raw milk, pasteurization is generally expected to eliminate pathogens to a level that does not pose a risk to consumer health. However, pasteurization is different than complete sterilization; sterilization extends shelf life but is not required to ensure milk safety. While milk is pasteurized, not sterilized, this process has helped ensure the health of the American public for more than 100 years by inactivating infectious agents.
Nearly all (99%) of the commercial milk supply that is produced on dairy farms in the U.S. comes from farms that participate in the Grade “A” milk program and follow the Pasteurized Milk Ordinance (PMO), which includes controls that help ensure the safety of dairy products. Pasteurization and diversion or destruction of milk from sick cows are two important measures that are part of the federal-state milk safety system.
U.S Agency Response
Testing Results
In our May 10 update, we announced that all 297 samples from the FDA’s initial survey of retail dairy products were found to be negative for viable Highly Pathogenic H5N1 Avian Influenza (H5N1 HPAI) virus. Today, for continued transparency, the FDA is providing additional information on our retail sample survey.
The samples taken as part of this survey were collected at retail locations in 17 states by milk specialists in the FDA’s Office of Regulatory Affairs. USDA Agricultural Research Service’s U.S. National Poultry Research Center (ARS) analyzed these samples using stepwise, scientific methods. This testing included first conducting quantitative real time polymerase chain reaction (qRT-PCR) screening to determine if any of the retail samples contained H5N1 viral nucleic acid. The samples that were found to contain viral nucleic acid during qRT-PCR screening were followed with gold-standard egg inoculation testing conducted by ARS to determine if they contained live virus. None of the samples were positive for live virus. ARS scientists are currently obtaining peer review of their analysis as a first step to publishing these results.
While the FDA collected the 297 samples at retail locations in 17 states, these retail samples represent products produced at 132 processing locations in 38 states. The information in the first chart below shows the state in which the product was processed. Because the intent of our study was to assess a variety of products, samples were selected to be representative of processors in states that have been reported to have impacted dairy cattle and those that have not. Of note, the location of where milk was processed does not indicate where the milk was produced. This is because milk could be produced from cows on a farm or farms a few states away, processed (pasteurized) in a different state, and then be available for purchase in yet another state.
The charts below provide additional details on the samples taken as part of our survey of retail dairy products.
As noted previously, qRT-PCR-positive results do not necessarily represent live virus that may be a risk to consumers. Therefore, viability testing by egg inoculation was performed on the qPCR samples that were positive for viral nucleic acid. All of these samples did not detect any viable virus. If samples tested by qRT-PCR were negative, no further testing was performed since those samples did not contain HPAI viral nucleic acid. These findings further support our assessment that the milk safety system including pasteurization is effective against this virus and that the commercial milk supply remains safe.
Retail samples were collected between April 18-22 and represent a snapshot in time. This testing did not detect any live, infectious virus.
Table 1: Breakdown of Retail Sample Results by State Where Milk Was Processed
| State Where Milk Was Processed (May Not Relate to Where Milk Was Produced) | Detection of Live Virus in Retail Product(s) | Number of Retail Product Samples Tested | Retail Product Samples Negative for Viral RNA (qRT-PCR Screening -) | Retail Product Samples Positive for Viral RNA (qRT-PCR Screening +) | Retail Product Sample Results for Live Virus (Viability Testing by Egg Inoculation) |
|---|---|---|---|---|---|
| AR | No | 5 | 0 | 5 | 0 |
| AZ | No | 5 | 4 | 1 | 0 |
| CA | No | 21 | 21 | 0 | Not Performed (Negative qRT-PCR) |
| CO | No | 8 | 5 | 3 | 0 |
| CT | No | 2 | 2 | 0 | Not Performed (Negative qRT-PCR) |
| FL | No | 10 | 9 | 1 | 0 |
| GA | No | 8 | 8 | 0 | Not Performed (Negative qRT-PCR) |
| IA | No | 11 | 11 | 0 | Not Performed (Negative qRT-PCR) |
| ID | No | 4 | 4 | 0 | Not performed (Negative qRT-PCR) |
| IL | No | 5 | 5 | 0 | Not Performed (Negative qRT-PCR) |
| IN | No | 9 | 8 | 1 | 0 |
| KS | No | 7 | 1 | 6 | 0 |
| KY | No | 4 | 1 | 3 | 0 |
| MA | No | 4 | 4 | 0 | Not Performed (Negative qRT-PCR) |
| ME | No | 2 | 2 | 0 | Not Performed (Negative qRT-PCR) |
| MI | No | 13 | 9 | 4 | 0 |
| MN | No | 16 | 13 | 3 | 0 |
| MO | No | 10 | 7 | 3 | 0 |
| NC | No | 5 | 4 | 1 | 0 |
| ND | No | 2 | 2 | 0 | Not Performed (Negative qRT-PCR) |
| NE | No | 3 | 3 | 0 | Not Performed (Negative qRT-PCR) |
| NH | No | 1 | 1 | 0 | Not Performed (Negative qRT-PCR) |
| NJ | No | 3 | 3 | 0 | Not Performed (Negative qRT-PCR) |
| NV | No | 4 | 4 | 0 | Not Performed (Negative qRT-PCR) |
| NY | No | 38 | 38 | 0 | Not Performed (Negative qRT-PCR) |
| OH | No | 8 | 5 | 3 | 0 |
| OK | No | 12 | 2 | 10 | 0 |
| OR | No | 10 | 10 | 0 | Not Performed (Negative qRT-PCR) |
| PA | No | 2 | 2 | 0 | Not Performed (Negative qRT-PCR) |
| SC | No | 3 | 0 | 3 | 0 |
| TN | No | 3 | 3 | 0 | Not Performed (Negative qRT-PCR) |
| TX | No | 26 | 13 | 13 | 0 |
| UT | No | 5 | 5 | 0 | Not Performed (Negative qRT-PCR) |
| VA | No | 6 | 6 | 0 | Not Performed (Negative qRT-PCR) |
| VT | No | 2 | 2 | 0 | Not Performed (Negative qRT-PCR) |
| WA | No | 8 | 8 | 0 | Not Performed (Negative qRT-PCR) |
| WI | No | 11 | 11 | 0 | Not Performed (Negative qRT-PCR) |
| WV | No | 1 | 1 | 0 | Not Performed (Negative qRT-PCR) |
Table 2: Breakdown of Retail Sample Results by Product Type
| Product Category | Number of Retail Product Samples | Detection of Live Virus in Retail Product | Retail Product Samples Negative for Viral RNA (qRT-PCR Screening -) | Retail Product Samples Positive for Viral RNA (qRT-PCR Screening +) | Percent of Retail Product Samples Positive for Viral RNA (via qRT-PCR screening) | Retail Product Sample Results for Live Virus (Confirmatory Virus Culture) |
|---|---|---|---|---|---|---|
| Skim Milk | 36 | No | 32 | 4 | 11.1% | 0/4 |
| 1% Milk | 28 | No | 19 | 9 | 32.1% | 0/9 |
| 2% Milk | 58 | No | 42 | 16 | 27.6% | 0/16 |
| Whole Milk | 68 | No | 52 | 16 | 23.5% | 0/16 |
| Cottage Cheese | 21 | No | 20 | 1 | 4.8% | 0/1 |
| Cream | 17 | No | 14 | 3 | 17.6% | 0/3 |
| Half and Half | 25 | No | 19 | 6 | 24.0% | 0/6 |
| Sour Cream and Similar | 30 | No | 25 | 5 | 16.7% | 0/5 |
| Yogurt | 14 | No | 14 | 0 | 0 | NA |
| Total | 297 | None | 237 | 60 | 20.2% | 0/60 |
This retail sampling study was designed to assess the effectiveness of the PMO milk safety system; it was not designed to assess the prevalence of H5N1 in dairy herds. It is important to underscore that milk purchased for the retail study in a particular state does not mean that it was produced or processed in that state. Commercial milk is typically pooled from many dairy farms, pasteurized in bulk and distributed to a variety of states. Even if a sample was collected in one particular state, the milk in a consumer package could have come from cows on several farms located in several states, pasteurized in a different state from the states where the milk was produced, and available for purchase in yet another state.
To further validate pasteurization effectiveness against the recently identified H5N1 virus, we are undertaking a pasteurization study designed to better replicate real-world conditions. Preliminary results from this work are expected in the near future.
Multiple tests are used to assess the safety of food items. Understanding how and why different methodologies are used and work, as well as how results fit into the larger picture, is critical to interpret any findings.
- Quantitative polymerase chain reaction (qRT-PCR) is a screening tool used to determine the presence or absence of an organism’s genetic material in a sample. A positive qRT-PCR means that the genetic material from the targeted pathogen was detected in the sample, but that does not mean that the sample contains an intact, infectious pathogen. That’s because qRT-PCR tests will also detect the residual genetic material from pathogens killed by heat, like pasteurization, or other food safety treatments. Importantly, additional testing is required to determine whether intact pathogen is still present and if it remains infectious, which determines whether there is any risk of illness associated with consuming the product.
- Embryonated Egg Viability Studies are considered the “gold standard” for sensitive detection of active, infectious virus. These studies are one of the types of additional tests necessary following PCR testing. These studies are done by injecting an embryonated chicken egg with a sample and then evaluating to see whether any active virus replicates. While this provides the most sensitive results, it takes a longer time to complete than other methods.
- Madin-Darby Canine Kidney (MDCK) Cell Culture is different type of additional test used following PCR testing to detect live, infectious virus. This is done by injecting a sample into specific tissue cells to determine whether any live virus is present and replicates. This method can usually be done more quickly than embryonated egg viability studies, but it is not as sensitive and may provide false negative results when the amount of virus in the sample is very low.
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