Key facts
- A fourth human case of highly pathogenic avian influenza (HPAI) A(H5), associated with the ongoing multi-state outbreak of A(H5N1) in dairy cattle in the United States, was reported on 3 July 2024 in the state of Colorado.
- As of 3 July 2024, there have been four human cases of avian influenza A(H5N1) reported in workers at dairy farms with infected cows (Texas (1), Michigan (2), Colorado (1)). The viruses isolated from the previous cases belonged to HA clade 2.3.4.4b, genotype B3.13. Results of genomic analysis are pending for the fourth case.
- To date, routine population-based surveillance has not detected any increase in community rates of respiratory infections.
- The outbreak of highly pathogenic avian influenza (HPAI) A(H5N1) in cattle is still ongoing, with 138 farms affected across 12 states of the US as of 3 July 2024.
Overview
Update: A fourth human case of highly pathogenic avian influenza (HPAI) A(H5), associated with the ongoing multi-state outbreak of A(H5N1) in dairy cattle in United States, was reported by US CDC on 3 July 2024 in Colorado. The dairy farm worker had exposure to infected cows, suggesting probable cow-to-human transmission. The patient reported eye symptoms only, received antiviral treatment (oseltamivir) and has recovered. The designation of the influenza virus neuraminidase (the N in the subtype) is pending genetic sequencing at CDC. Attempts to sequence the virus in the clinical specimen are underway and will be made available within 1-2 days if successful.
Based on the information available at this time, this infection does not change the CDC’s current H5N1 bird flu human health risk assessment for the US general public, which the Agency considers to be low. However, this development underscores the importance of recommended precautions in people with exposure to infected animals. People with close or prolonged, unprotected exposure to infected birds or other animals (including livestock), or to environments contaminated by infected birds or other animals, are at greater risk of infection.
On 1 April 2024, the first human case of HPAI A(H5N1) was reported in an individual who had prior exposure to dairy cattle presumed to be infected with HPAI A(H5N1) in Texas, US (US CDC). The virus isolated from this case belonged to the HA clade 2.3.4.4b of HPAI A(H5N1), genotype B3.13, and was closely related to the virus detected in dairy cattle in Texas. Genetic analysis revealed some changes in the virus sequence from the patient specimen compared to the viral sequences found in the cattle. The virus sequence from the human case displayed the PB2 E627K mutation, which is associated with viral adaptation to mammalian hosts. However, the virus remains avian-like (i.e. retaining a strong preference for avian and not mammalian receptors). There were no markers identified that are known to be associated with resistance to influenza antiviral medications.
On 22 May 2024, the US CDC reported the second human infection with avian influenza A(H5) in a farm worker in Michigan, associated with an ongoing multi-state outbreak of A(H5N1) in dairy cows. The farm worker was being monitored because of work exposure to A(H5N1) infected cattle. Similar to the previous human case of HPAI A(H5N1) reported on 1 April 2024 in Texas, the individual's only symptom was conjunctivitis. Two specimens were collected from the dairy farm worker after reporting symptoms of conjunctivitis to the local health authorities. The nasal specimen tested negative, while a sample from the eye was confirmed positive for A(H5N1) at the CDC laboratory. According to genomic analysis performed by US CDC, the virus identified belonged to HA clade 2.3.4.4b, genotype B3.13 (GISAID ID: EPI_ISL_19162802). The genome of the virus was closely related to viruses found in dairy cattle, suggesting cow-to-human transmission. The E627K mutation observed in the PB2 segment of the virus from the Texas case was not present. The genome of the virus from the Michigan case did, however, have the PB2 M631L change, which is associated with viral adaptation to mammalian hosts and has been observed in 99% of virus sequences from dairy cows, but only occasionally in birds. No markers of antiviral resistance were detected in the virus sequences from the Michigan case and the virus was closely related to existing HPAI A(H5N1) candidate vaccines.
A third human case of highly pathogenic avian influenza (HPAI) A(H5N1), associated with the ongoing multi-state outbreak of A(H5N1) in dairy cattle in the US, was reported by the US CDC on 30 May 2024 in Michigan. The dairy farm worker had exposure to infected cows, suggesting probable cow-to-human transmission. Unlike the previous two cases, the patient reported upper respiratory tract symptoms, including a cough but no fever, as well as eye discomfort with watery discharge. The patient received antiviral treatment (oseltamivir), is isolating at home, and their symptoms are resolving. Household contacts and other workers at the farm are being monitored, with no symptoms having been reported so far. Household contacts have been offered oseltamivir. There is no indication of human-to-human transmission of A(H5N1) viruses at this time. From publicly available sequences (GISAID ID: EPI_ISL_19177746), most segments were missing and the deposited HA segment was partial, which limited the possibility of determining mutations. However, a high similarity to the virus sequences from US cattle could be confirmed.
Michigan Department of Health and Human Services further mentioned that neither of the two cases reported in Michigan were wearing full personal protective equipment (PPE). The case reported on 22 May 2024 developed eye symptoms after having milk splashed in their eye, highlighting the importance of appropriate PPE. Since the three reported cases had direct contact with infected cattle, the US CDC's current assessment of the human health risk of A(H5N1) to the general public in the US does not change.
The United States' Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS) has detected viral particles of HPAI A(H5N1) in tissue samples, including muscle, from a culled dairy cow that had been condemned (declared unfit for consumption) during a post-mortem inspection due to signs of systemic disease. Dairy cattle slaughtered for beef production undergo routine inspection before and after slaughter by the FSIS. Meat from dairy cattle condemned at slaughter due to systemic disease do not enter the human food supply.
A study of ground beef inoculated with A(H5N1) suggested cooking burgers medium to well done (to a temperature of 63C to 71C) inactivated the virus, while cooking burgers to 49C (rare) also substantially inactivated the virus.
HPAI A(H5N1) virus has been detected in dairy cattle in several states in the US. As of 3 July 2024, the USDA reports the detection of HPAI A(H5N1) in 12 states, affecting 138 dairy farms/herds. The most recently reported detection was on 1 July 2024 in Colorado. Markers of influenza A(H5) have also been detected in wastewater in Texas (Tisza et al., 2024; Wolfe et al., 2024). Furthermore, cats fed unpasteurised milk and colostrum from affected cows developed systemic, fatal infection (Burrough et al., 2024).
HPAI A(H5N1) has also been reported in some other mammals in the US, including goats and alpacas at farms with infected poultry. The virus genotype identified in the infected goats was different to the one identified in cattle (B3.13), while a virus from the same genotype B3.13 had infected the alpacas.
Genetic material of HPAI A(H5N1) has been detected in milk samples. Studies performed by US FDA have shown that pasteurisation inactivates HPAI in milk and dairy products, with no viable virus being detected following pasteurisation. For further information, please refer to the US FDA update. Samples of ground beef from states with affected dairy herds tested negative for HPAI A(H5N1) (USDA).
ECDC assessment
Based on available information, the World Health Organization, the Food and Agriculture Organization of the United Nations and the World Organisation for Animal Health have assessed the overall public health risk posed by A(H5N1) to be low, and for those exposed to infected animals or contaminated environments, the risk of infection is considered low-to-moderate. The US CDC has also stated that the overall threat of HPAI A(H5N1) clade 2.3.4.4b to the general public in the US remains low. However, individuals with close or prolonged exposure to infected animals or contaminated environments are considered at greater risk of infection. The USDA and US FDA highlight that commercially produced, pasteurised milk is safe for consumers and recommend that milk from cattle with clinical signs of infection is removed from the human food chain.
In the latest joint ECDC/EFSA/EURL monitoring report, ECDC assessed the risk of infection from the circulating HPAI A(H5N1) clade 2.3.4.4b viruses as low for the general population and low-to-moderate for those with activities that expose them to infected animals or a contaminated environment (e.g. occupationally exposure to infected animals). To date, there have been no confirmed cases of A(H5N1) infection in humans and no reports of A(H5N1) infection in cattle in the EU/EEA. The genotype B3.13 identified in cattle and the human case in the US has not currently been detected in Europe. The current available evidence does not change the overall assessment of the risk for the EU/EEA population. ECDC is monitoring the situation together with partner organisations in Europe and will continue to update its assessment of the risk for humans in the EU/EEA accordingly as new information becomes available.
The EU Wastewater Observatory for Public Health has gathered information on ongoing wastewater surveillance for avian influenza in the EU, with 13 EU countries expressing interest for a coordinated approach. Twelve countries are running preliminary studies that can be upgraded. At present, HPAI A(H5N1) has not been detected in European (waste)water.
In addition to enhanced surveillance, active monitoring and testing of exposed individuals is recommended for early detection of human cases and to assess the possibility of human-to-human transmission, according to the relevant ECDC guidance documents (Testing and detection of zoonotic influenza virus infections in humans; Investigation protocol of human cases of avian influenza virus; Enhanced surveillance of severe avian influenza virus infections in hospital settings). Given the uncertainties related to mammal-to-mammal transmission and depending on the epidemiological situation, a low threshold can be considered for testing individuals exposed to potentially infected mammals (for example symptomatic individuals with conjunctivitis or respiratory symptoms). Due to the higher risk of infection for individuals exposed to infected animals and contaminated environments, appropriate personal protective measures and other precautionary measures should always be taken to reduce the risk of infection.
ECDC relevant publications:
- Testing and detection of zoonotic influenza virus infections in humans in the EU/EEA, and occupational safety and health measures for those exposed at work
- Enhanced influenza surveillance to detect avian influenza virus infections in the EU/EEA during the inter-seasonal period
- Investigation protocol of human cases of avian influenza virus infections in the EU/EEA
- Joint ECDC-EFSA Drivers for a pandemic due to avian influenza and options for One Health mitigation measures
Actions
ECDC is in contact with the US Centers for Disease Control and Prevention (CDC) for further information and is closely following any updates on the event. ECDC monitors avian influenza strains through its influenza surveillance programme and epidemic intelligence activities in collaboration with the European Food Safety Authority (EFSA) and the EU Reference Laboratory for Avian Influenza in order to identify significant changes in the virological characteristics and epidemiology of the virus. Together with EFSA and the EU Reference Laboratory for Avian Influenza, ECDC produces a quarterly updated report of the avian influenza situation.