WAILUKU, Maui — Health officials are warning of a recent spate of food-poisoning cases on Maui linked to Spam musubi, a popular snack-on-the-go and home-lunch staple for countless Hawai'i schoolchildren.

Two adults and seven children, ages 3 to 9, have been sickened since July after eating Spam musubi purchased at two or three different stores, said Dr. Lorrin Pang, Maui district health officer for the state Department of Health. None required hospitalization.

He said no health citations were issued to the food preparers or retailers because it is unclear whether the problem occurred from improper preparation or storage, or because consumers let the musubi sit for hours at room temperature, thereby spurring bacterial growth.

The food poisoning was traced to staphylococcal and bacillus cereus bacteria, which cause acute gastrointestinal illness characterized by a sudden onset of vomiting, diarrhea and abdominal cramping. Symptoms usually disappear within 24 hours.

Many people think Spam is impervious to spoiling because of the heavy dose of preservatives it contains. Pang said the bacterial growth is more likely to occur on the rice rather than on the processed meat product.

Stores are required to keep Spam musubi, sushi, bentos and similar ready-to-eat items at safe warm and cool temperatures — at least 140 degrees Fahrenheit, or below 45 degrees. Perishable food items kept at room temperature near a store cash register or on a shelf should be eaten within four hours of preparation, Pang said. Consumers can check time labels to determine when an item was made.

Pang said it's OK to stash fresh musubi in a chilled lunchbox for several hours, but most people prefer to keep it at room temperature, inviting food poisoning. "Have you ever eaten cold Spam musubi?" he asked.

Spam musubi was blamed for a November outbreak of food poisoning traced to several outlets of a Maui convenience store chain that purchased its rice from an outside source. Seven children were reported ill in that incident.

Suspected cases of food poisoning should be immediately reported by calling county district health offices.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.