U.S. officials say they are working to step up global efforts to detect and contain outbreaks of the bird flu virus as soon as they occur. The virus has so far infected 174 people and spread to birds in more than 30 countries.

Four of the top U.S. public health officials testified Thursday before a House Appropriations Committee subcommittee. Their basic message was the same - contain a potential human bird flu pandemic as soon as possible, before it comes to the United States.

The U.S. Agency for International Development's Kent Hill said he is concerned the chances for the virus to infect humans increases as it moves around the world.

"With the spread of the number of countries that have significant outbreaks of some sort, obviously there's more contacts with human beings, and that increases the likelihood, or possibility, I should put it, of something happening that we don't want to happen, which is, of course, a human global pandemic."

He said accurate surveillance of bird flu outbreaks is crucial to global efforts to combat the virus. As an example, he pointed to Nigeria.

"On January 10th, they reported massive bird die-offs, but they were misdiagnosed as to the cause. It was not until February that it was confirmed internationally that, indeed it was H5N1. So, several weeks had passed before they even realized what had happened. That was several weeks in which the spread could occur. It's no mystery why, this week, it appeared in Niger, just to the north. So, we think it's probably in many places in Africa already."

The Centers for Disease Control and Prevention director Julie Gerberding told the subcommittee that her agency is among those helping other countries that need it develop a public health system able to detect bird flu.

"There are a lot of black boxes out there, where something could emerge, and it's going to take us a while to find it. We'll plug them as quickly as we can, but we just don't have a seamless network yet. And we're only as strong as our weakest link."

In order to mobilize a faster response, she added that her agency is in the process of building 18 regional centers around the world.

"We have several of them already, including one in Kenya. And when the problems emerged in Nigeria, CDC was able to send its Kenyan response team over to Nigeria to be on the ground much more quickly than we could get people from Atlanta [CDC Headquarters], there to assist with the WHO response capability."

Meanwhile, the State Department's Nancy Powell said the United States, Canada and Mexico are discussing what they will do should there be a bird flu outbreak in North America.