State investigators are looking into the choking death of a developmentally disabled patient at Queens Hospital Center who — despite being on a strict puree diet — was given a sandwich by staff, the Post has learned.

Wendy Alexander, 49, was admitted to the psychiatric emergency room in January because she became agitated at her group home, according to a letter penned by anonymous hospital nurses.

Alexander’s aide informed the hospital about her dietary limitations, but she was still placed on a regular diet, the letter says.

A nurse caught the mistake and ordered pureed food, but the error was never reversed in the computer system.

When Alexander, who was heavily medicated, woke up in the night and wanted food, a new nurse was unaware of her dietary restriction and gave the handicapped woman a sandwich to eat, the concerned message says.

Alexander started to choke and went into cardiac arrest after an “inexperienced” resident doctor delayed treating her, according to the letter.

She was transferred to the regular emergency room and she died on Jan. 17.

“This was a tragic event that could and should have been prevented,” the letter reads.

The state Department of Health confirmed that “an incident involving a choking death of a patient at Queens Hospital Center was reported to DOH. DOH is reviewing the incident and will take appropriate action.”

Hospitals are supposed to report “adverse events” to the DOH within 24 hours.

The city Medical Examiner’s Office is also investigating Alexander’s death, saying, “The cause and manner of death are pending further studies.”

The city’s Health and Hospitals Corp., which runs Queens Hospital Center, said it couldn’t comment on individual cases.

“We take all allegations regarding patient care very seriously and meet all reporting requirements with state and federal regulatory agencies to ensure claims are properly addressed,” according to an HHC statement.