A nursing home houses 120 residents. At the beginning of the month of April, 10 residents already have salmonellosis, a gastrointestinal illness caused by the bacterium Salmonella, which typically spreads through contaminated food or water and causes diarrhea, fever, and abdominal cramps. During the entire month of April, 18 new cases of salmonellosis are confirmed among residents who were not already sick at the start of the month. By the last day of April, 12 residents in total are still actively sick with salmonellosis (this includes 2 carried over from the original 10 cases at the start of the month, and 10 from the 18 new cases identified during April).
What was the incidence proportion of salmonellosis in the nursing home during the entire month of April?
