In the NICU outbreak, what was the attack rate among parents?

• A. 20%
• B. 25%
• C. 40%
• D. 50%

Answer: (C)

Attack rate is the proportion of people at risk who become infected during an outbreak, calculated as the number of new cases in the group divided by the total number of people in that group who were at risk. In the NICU outbreak, 40% of the parents who were exposed showed infection or colonization, meaning that roughly four out of ten parents involved in the outbreak acquired the pathogen through contact with the infants. This reflects how transmission can occur via close parental interaction in the NICU, underscoring the importance of strict hand hygiene, proper use of gloves and gowns, and visitor management to limit spread. If, for example, 10 parents were exposed and 4 became cases, the attack rate would be 4/10, or 40%. The other percentages would imply different counts of cases among the same at-risk group, which does not match the observed data.