After measles exposure, if the initial titer is 1:20, what is the recommended next step?

After measles exposure, if the initial titer is 1:20, what is the recommended next step?

• A. The test should be repeated in 10 days to 2 weeks
• B. Begin antiviral therapy
• C. Immediately isolate the patient
• D. Repeat the test in 6 months

Answer: (A)

Serology for measles is interpreted with paired samples because a single low titer after exposure doesn’t distinguish between early infection, waning immunity, or true immunity. An initial titer of 1:20 isn’t diagnostic on its own, so the next step is to obtain a convalescent specimen about 10 to 14 days after exposure and look for a fourfold (or greater) rise in measles-specific antibodies. A significant rise between the acute and convalescent samples indicates recent infection or an immune response, whereas no rise makes active infection unlikely. Antiviral therapy isn’t used for measles, and immediate isolation decisions depend on clinical symptoms and public health guidance rather than a single early titer. In short, repeat testing in the 10–14 day window to detect seroconversion is the appropriate next step.

Serology for measles is interpreted with paired samples because a single low titer after exposure doesn’t distinguish between early infection, waning immunity, or true immunity. An initial titer of 1:20 isn’t diagnostic on its own, so the next step is to obtain a convalescent specimen about 10 to 14 days after exposure and look for a fourfold (or greater) rise in measles-specific antibodies. A significant rise between the acute and convalescent samples indicates recent infection or an immune response, whereas no rise makes active infection unlikely. Antiviral therapy isn’t used for measles, and immediate isolation decisions depend on clinical symptoms and public health guidance rather than a single early titer. In short, repeat testing in the 10–14 day window to detect seroconversion is the appropriate next step.