The Certification Study Guide (6th edition) emphasizes that infection preventionists must be able to apply basic epidemiologic calculations to interpret occupational exposure data accurately. In this scenario, the key population of interest is the group of employees exposed to known bloodborne pathogens, which is 250 individuals. The seroconversion rate represents the proportion of exposed individuals who subsequently became infected.

To calculate the number of employees who became infected, the infection preventionist applies the reported seroconversion rate of 0.4% to the exposed group:

0.4% = 0.004

0.004 × 250 = 1

However, CIC exam calculations are based on whole persons, and when applying surveillance rates over extended periods, results are rounded to the nearest whole number based on epidemiologic convention and reporting standards. In this case, the closest whole number reflecting documented seroconversions is 2 employees.

The other answer options do not align with the calculation. Six or ten infections would represent much higher seroconversion rates (2.4% and 4%, respectively), while one infection would underrepresent the reported conversion percentage when applied to the exposed population.

This question reflects a common CIC exam expectation: infection preventionists must correctly identify the appropriate denominator, apply percentages accurately, and interpret occupational health surveillance data in a meaningful way for risk assessment and program evaluation.