The H5N1 bird flu virus made headlines two years ago as the world worked to head off a potential disaster. The disease continues to decimate poultry stocks and human deaths still occur sporadically, but the public has largely lost interest because the virus has not mutated into a much-feared form that could spread easily among people.

“Emerging infectious diseases are a major global public health threat, and there’s nothing in the world of evidence that would suggest that the threat is getting smaller,” Dr. Julie Gerberding, head of the U.S. Centers for Disease Control and Prevention, told a health conference in Malaysia.

“A pandemic would be a catastrophic human health event if it had any of the characteristics of the previous pandemics in terms of transmissibility and case fatality rate,” she said.

Although much progress has been made in preparing for a possible flu pandemic, “the bad news is, it’s a long way to go,” Gerberding added.

She urged people to remain vigilant.

“Public health enemy No. 1 is the challenge of complacency and our inability to maintain a focus on threats when they are around the corner or potentially in our backyard,” Gerberding said.

She said people also should pay more attention to the ways that climate change will affect health. Some areas of the world will be inundated with water, while others will face a scarcity. Food security will become a bigger problem, while mosquito-borne diseases are likely to spread to new areas, she said.

Gerberding said events in her own backyard forced her to think about just how closely people, animals and the environment are linked and how many people do not make the connection until they are directly affected.

“Three years ago, my husband was mowing the lawn on a Tuesday night and acquired a West Nile virus infection and developed encephalitis in my backyard — literally,” she said in her speech at the three-day International Congress on Infectious Diseases. “A year ago, I adopted a stray cat that I found in this backyard … but amazingly she was carrying cat-scratch disease and I acquired it from her.”

Bird flu has killed at least 243 people worldwide since it began ravaging Asian poultry stocks in late 2003. The disease remains hard for people to catch, with most human cases linked to contact with infected birds. Indonesia remains the worst-hit nation with 110 deaths, and continues to receive global criticism for failing to regularly share bird flu virus specimens with the World Health Organization. The country also has recently stopped reporting deaths to the public at the time they occur.

“It is a very small world and as we prepare, our preparedness is only as strong as its weakest link,” Gerberding said, adding that every country must share virus information to allow scientists to monitor any changes.