Nearly half the 50 students and adults from the Bayport-Blue Point school district who went on a school trip to Spain last month returned with symptoms consistent with the norovirus, Suffolk County health officials said Friday.

Of the 44 students and six adults who went on the trip from April 21 to April 30, 24 came down with the symptoms, including two who were hospitalized and treated, said Grace Kelly-McGovern, a spokeswoman for the Suffolk County Department of Health Services.

Only one person who made the trip has been tested for norovirus, Kelly-McGovern said, and that test result had not been returned from the lab to the health department as of noon Friday.

A spokeswoman for the school district said nine students from the trip went to the hospital and were treated, mostly for dehydration.

Since the students returned from Spain, 19 other students who did not go on the trip also have had symptoms of the virus, the district said.

Gaurav Passi, principal of Bayport-Blue Point High School in Bayport, inadvertently said in a letter earlier this week that district students had contracted the virus. The district later said the students only had displayed symptoms of the virus.

Both the district and health department reiterated Friday that testing has yet to confirm any of the students had been infected.

Passi’s letter to parents and students said the source of the illness was possibly a contaminated “bottled water source provided abroad.”

District officials have spoken to all the students who went on the trip and the county health department had been notified, Passi said in the letter.

Classrooms in the school were cleaned on Thursday night, and the remaining rooms in the high school are scheduled to be cleaned starting Friday night and possibly into the weekend, the district said.

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The letter said some of the ailing students were slated to take Advanced Placement exams and school officials offered to reschedule those tests.

According to the Center for Disease Control and Prevention, norovirus is highly contagious and causes inflammation of the stomach or intestines or both. Common symptoms are stomach pain, nausea, diarrhea and vomiting.

Norovirus is the most common cause of acute gastroenteritis in the United States, and it is the most common cause of foodborne-disease outbreaks.