Measles occurs in a household of 8 susceptible contacts following introduction of an index case. Three of these 8 contacts develop measles within the incubation period. The secondary attack rate of measles in this household is:

• A 37.5 per cent ✓
• B 33.3 per cent
• C 42.9 per cent
• D 30 per cent

Explanation

Secondary attack rate equals the number of secondary cases divided by the number of susceptible individuals exposed to the index case, multiplied by 100. Here it is 3 out of 8 contacts, giving 37.5 percent. The index case is excluded from both numerator and denominator. Option B incorrectly divides by 9 total household members including the index case, and option C wrongly subtracts the three secondary cases from the denominator.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.