When should a pregnant dietician, who visited a patient with morbilli (measles) while wearing a surgical mask and hand gloves, undergo serological testing for IgM (Immunoglobulin M) and IgG (Immunoglobulin G) antibodies to determine her immune status?

Immediate Serological Testing for Measles Immunity Status

Check the pregnant dietician's measles immunity status immediately (within 24-48 hours of exposure) by testing for measles IgG antibodies to determine if she has presumptive evidence of immunity, and if she lacks documented immunity, she should be excluded from work from day 5 through day 21 post-exposure. 1

Immediate Post-Exposure Management Algorithm

Step 1: Assess Immunity Status Immediately After Exposure

• All healthcare workers exposed to measles must be evaluated immediately for presumptive evidence of measles immunity 1
• Acceptable evidence of immunity includes:
  • Written documentation of 2 doses of MMR vaccine administered at least 28 days apart 1
  • Laboratory evidence of immunity (IgG antibodies) 1
  • Laboratory confirmation of prior disease 1
  • Birth before 1957 (though this is less reliable for healthcare workers) 1

Step 2: Testing Timeline for Non-Immune or Unknown Immunity Status

For immunity assessment (IgG testing):

• Test immediately to determine baseline immunity status 1
• IgG antibodies indicate past infection or vaccination and provide evidence of immunity 1

For infection diagnosis if she develops symptoms (IgM testing):

• Measles IgM antibodies are most reliably detected 6-14 days after symptom onset, with seropositivity rates of 92-100% 2
• If clinical suspicion is high but initial IgM is negative, collect a second specimen at least 72 hours after rash onset 2
• IgM testing is most sensitive when collected at the time of rash onset 2

Step 3: Work Restriction Based on Immunity Status

If she lacks documented immunity:

• Exclude from work from day 5 through day 21 after exposure, even if she receives post-exposure immune globulin 1
• Offer first dose of MMR vaccine immediately (though contraindicated in pregnancy, this applies to non-pregnant healthcare workers) 1

If she has documented immunity (2 doses of MMR or positive IgG):

• She may continue working but must observe airborne precautions when caring for measles patients 1
• Despite documented immunity, there is a ~1% vaccine failure rate, so all healthcare workers should use N95 respirators with measles patients 1

Critical Pregnancy-Specific Considerations

MMR Vaccination Contraindication

• MMR vaccine is absolutely contraindicated during pregnancy 3
• If she is non-immune, she cannot receive post-exposure MMR vaccination 3
• She should receive intramuscular immune globulin 0.25 mL/kg (40 mg IgG/kg) if non-immune and exposed 1

Post-Exposure Prophylaxis Window

• Immune globulin must be administered within 6 days of exposure to be effective (based on general medical knowledge of measles post-exposure prophylaxis)
• Even with immune globulin, work exclusion from day 5-21 post-exposure is still required 1

Monitoring for Disease Development

If she develops measles-compatible symptoms:

• Isolate immediately and implement airborne precautions 1
• Test for measles IgM antibody as the first-line diagnostic test 2
• Exclude from work until ≥4 days following rash onset if measles develops 1

Common Pitfalls to Avoid

• Do not wait for symptoms to develop before assessing immunity status - immediate evaluation is critical 1
• Do not rely on surgical masks for protection - measles requires airborne precautions with N95 respirators 1
• Do not test IgM too early - false negatives occur if collected within first 72 hours of rash onset 2
• Do not assume immunity based on birth year alone for healthcare workers - 5-9% of those born before 1957 lack detectable measles antibody 1

Post-Delivery Planning

• If she is found to be non-immune, vaccinate with MMR immediately postpartum before hospital discharge 4
• Breastfeeding is not a contraindication to postpartum MMR vaccination 4
• Counsel to avoid pregnancy for 3 months after MMR vaccination 3, 4