The Columbus Health Department continues to investigate, but preliminary reports indicate no cause to suspect conditions at either the school or at the camp where the students and teachers spent three days in late October, according to Sherry Bjerke, the school nurse who serves Wilson Hill.

School officials called the health department last week after 13 people -- sixth-graders and one of their teachers -- became ill. Nine had pneumonia, four a viral respiratory illness.

The health department reported back on Friday that no common source of infection had been found. No staff members at Camp Templed Hills, where the schools' 72 sixth-graders had stayed Oct. 23-25, had become ill, said Wilson Hill principal Pat Reeder.

"At that point, there was no cause for alarm or reason we should do something different in our school environment," Bjerke said.

Still, surfaces typically used by students were disinfected over the weekend.

Some of the infected students returned to school this week, Reeder said.

Bjerke said the students and staff probably infected each other because they were living in such close proximity at the camp. Respiratory illnesses are spread when someone infected sneezes or coughs and the droplets come into contact with another person.

Students are being reminded of the importance of hand washing, Reeder said in one of the letters she sent to Wilson Hill parents last week.

The story was reported by a local television station last week, then was picked up by CNN over the weekend. School officials said they were surprised at the interest.

"It kind of snowballed," Bjerke said.