Parameters:
(1) number of patients with a specified type of infection
(2) total number of patients at risk
(3) time interval in months over which data collected
(4) total number of days of a risk exposure (sum of days of exposure for all patients at risk)
simple infection rate =
= (number who develop an infection) / (number at risk)
infection rate per 1000 days of exposure risk =
= (number infected) / ((total number of days of exposure) / 1000)
where:
• Risk exposure may be related to the use of an indwelling urinary catheter, intravascular catheter, mechanical ventilation, etc).
annualized infection rate =
= (infection rate for time interval) / ((time interval in months) / 12)
The infection rate may be affected by a number of factors such as disease severity or hospital setting. The rate of infection for a hospital should be compared to the rates seen at hospitals of similar size and setting.
