Tap water tainted with salmonella has sickened nearly 140 people in Alamosa, a small town in Colorado, health officials confirmed Saturday.

Among those infected, seven have been hospitalized for treatment, authorities said.

The incident prompted Colorado Governor Bill Ritter to declare an emergency, activate the National Guard and provide as much as 300,000 U.S. dollars for response efforts.

The city and county have also declared emergencies as officials scrambled to provide safe water and disinfect the system with chlorine.

An analysis indicated the municipal water system in Alamosa is the source of the bacterial outbreak, as suspected, said Ned Calonge, chief medical officer for the state health department.

As of Friday, 138 cases of salmonella linked to the outbreak had been reported in people from infancy to age 89, of which 47 were confirmed by lab testing, Calonge said. The conditions of those hospitalized weren't released.

It remained unknown how the system was contaminated. Possibilities include a compromise in a storage tank or cross-contamination with a sewage line, Calonge said.

It could be three more weeks before residents of the southern Colorado town can drink water straight from the tap, according to the state health department.

The earliest the city water system could be flushed is Tuesday, and disinfecting it and making sure it is safe could take many days, said James Martin, executive director of the department.

Boiling tap water will kill bacteria, but health officials warned that no one should use even boiled tap water once the flushing of the water system begins. People were warned not to give pets tap water, either.

Alamosa, with about 8,500 residents, gets its water from a deep well system. The water is pure from the aquifer and is not chlorinated.

The incident was among the most serious water contamination in the nation over the past few years. The nation reported only 15 salmonella outbreaks from public water systems from 1971 to 2004, according to statistics released by the federal Centers for Disease Control and Prevention.

Experts said the incident sounded an alarm to the nation's water security as the World's Water Day was marked in parts of the nation on Saturday.

Symptoms of salmonella include diarrhea, fever and stomach cramps that usually go away within a week, although same cases may require hospitalization.

(Xinhua News Agency, March 23, 2008)