Two outbreaks of salmonella poisoning linked to the nation’s sixth-largest chicken producer, Foster Farms, may have sickened as many as 15,000 people this year, which highlighted significant weaknesses in government food safety oversight, a new report finds. The USDA failed to adequately notify consumers of possible hazards, didn’t demand recalls of potentially tainted chicken parts and allowed poultry producers to continue shipping the meat to stores, despite evidence of contamination, according to a report by the Pew Charitable Trusts released Thursday. The agency relies on limits for salmonella contamination in chicken, known as “performance standards,” that are either outdated or, in the case of chicken parts, non-existent, the report says. And FSIS tests products at chicken plants just once a year, except for plants considered “best-performing” — like Foster Farms — which are tested every other year, with advance warning of the inspections.