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

• A. 45%
• B. 55%
• C. 60%
• D. 70%

Answer: (B)

Attack rate measures how widely an outbreak spreads among people at risk during a defined period. It’s calculated as the number of employees who developed illness during the outbreak divided by the total number of employees at risk, times 100. In this NICU outbreak, the data correspond to 55%, meaning just over half of the staff at risk became ill. For example, if 11 of 20 employees were affected, the rate would be 11/20 × 100 = 55%. This figure helps gauge transmission intensity and guides infection prevention actions such as reinforcing hand hygiene, appropriate use of PPE, cohorting or isolating affected staff, and targeted surveillance.