**First Bird Flu Case in California Reported Amid Rising Concerns of Human-to-Human Transmission**

Authorities in California have reported a presumptive positive case of the H5N1 bird flu in a dairy worker, potentially marking the state's first human infection. The patient, who remains unidentified, works at a dairy facility currently battling an outbreak of the avian influenza virus among its cattle. The individual has experienced mild symptoms, notably conjunctivitis or red eyes, and is presently receiving antiviral treatment while isolating at home.

The California Department of Public Health (CDPH) indicated that while the general risk of H5N1 to the public remains low, individuals with extensive contact with birds and livestock are more susceptible. This case is notably significant as it contributes to the growing fear of possible human-to-human transmission of the virus. These concerns have intensified following a case in Missouri where a patient, who had no direct contact with infected animals, tested positive for H5N1.

In Missouri, the patient was identified through the state's seasonal flu surveillance system, which tests symptomatic individuals for influenza activity. One hypothesis is that this patient might have contracted the virus by consuming raw milk containing H5N1, as studies have shown the virus can persist in refrigerated raw milk for up to five weeks.

The Centers for Disease Control and Prevention (CDC) recognizes the pandemic potential of bird flu, especially considering the H5N1's rapid mutation rate of approximately 300 times. Since March 2024, the CDC has monitored over 4,900 individuals exposed to infected animals, with more than 230 people tested and 14 confirmed positive cases to date. The latest possible case from California would be the 15th.

Earlier this year, a similar case was reported from Texas, where a dairy farmer also contracted the virus, showing symptoms that included conjunctivitis. According to a case report in the New England Journal of Medicine, the infection in the Texas patient began in the right eye and eventually spread to the left. He also experienced a subconjunctival hemorrhage and watery discharge from the eyes – symptoms consistent with H5N1 infection.

The H5N1 strain of bird flu first emerged in North America in early 2022 and has since caused significant mortality among poultry. The virus has also spread to various wild mammals, including cows, cats, and alpacas across nearly a dozen states, impacting over 39 herds based on available data. Globally, nearly 900 human cases have been documented over the past two decades, all linked to interaction with wild or domesticated birds.

With researchers cautioning about the possible broader spread of the virus, the situation remains closely monitored, particularly as the potential for person-to-person transmission poses a new level of threat.