A new salmonella outbreak linked to backyard poultry has sickened at least seven people in six states, health officials said Monday.

Two cases were identified in Missouri, and one each in Florida, Illinois, South Dakota, Utah and Wisconsin, the Centers for Disease Control and Prevention said.

People got sick in February and March of this year, the CDC said. They all had the same strain of salmonella — a version that has been traced to hatcheries in the past. The investigation is continuing, health officials said.

Salmonella bacteria cause about 1.35 million infections in the United States every year, and recent outbreaks have been tied to sources such as cucumbers, eggs, unpasteurized milk, fresh basil, geckos and pet bearded dragons.

But one concern is that chickens and other backyard poultry can carry salmonella bacteria even if they look healthy and clean. A backyard poultry-associated outbreak that ended last year was tied to 470 cases spread across 48 states, including one death.