WINSLOW (AP) - At least five workers at a poultry vaccination plant fell ill from salmonella exposure late last year, underscoring risks associated with the manufacture of veterinary products, the national Centers of Disease Control and Prevention reported Thursday.

As many as 21 workers reported symptoms consistent with salmonella exposure in the one-month period following a spill of liquid containing salmonella in November, but only five workers were confirmed through tests to have been exposed to salmonella, the CDC in Atlanta said. None of the sickened workers at Lohmann Animal Health International required hospitalization.

Salmonella, which sickens about 40,000 people and kills about 600 each year in the United States, causes diarrhea, fever, dehydration, abdominal pain and vomiting.

The Lohmann plant maintained cultures of four strains of salmonella for use in poultry vaccinations, and investigators believe the exposure began after a fermentation device in which a colony of salmonella was growing spilled over on Nov. 9.

The worker who discovered the spill in the restricted-access room cleaned up using a bleach solution and a commercial disinfectant, but then disposed of materials and sterilized the mop in another room that was used by many workers.

The investigation by the Maine CDC points to the room where the items were disposed of as being the probable source of the illnesses, said Anthony Yartel, infectious disease epidemiologist with the state CDC in Augusta.

Samples from several sickened workers were traced back to the same strain of salmonella that had spilled, said Yartel, lead author of the CDC report.

Though there were no conclusive determinations, the Maine CDC believes some workers were sickened by contact in the room where the material were disposed of, and that others were later sickened by person to person contact.

Among the recommendations after the incident was putting cleanup kits in each of the rooms where spills were likely could occur and additional protective equipment for some workers.

Lohmann Animal Health, which makes a wide variety of poultry vaccinations that are shipped to 50 countries, has implemented those changes to ensure that a similar incident doesn't happen in the future, said Lynn Clark, human resources manager.

The company, which employs 86 workers, continues to grow, Clark said Thursday. Earlier this month, it held a grand opening in Winslow after consolidating its transportation hub and manufacturing plant.