Call before you collect: Contact MDHHS Division of Immunization at 517-335-8159 or your LHD before submitting specimens. Testing is prioritized for cases with high clinical or epidemiologic suspicion.
Collect both viral specimens (PCR) and serum (IgM) at the same visit to avoid missed opportunities.
Viral specimens (PCR) — preferred
- Nasopharyngeal or throat swab, ideally within 3 days of rash onset; no later than 10 days post-rash onset. Submit in viral transport media (VTM).
- Also collect urine if more than 72 hours have elapsed since rash onset. Urine is most useful between days 5 and 9 after rash onset and should not replace the throat or NP swab — collect both. Do not collect urine if more than 10 days have passed since rash onset.
- Send to MDHHS Bureau of Laboratories (BOL). Turnaround: 48 hours or less for throat/NP swab; approximately 5 days for urine PCR.
Serum (IgM)
- Collect between day 3 and day 30 after rash onset (inclusive). IgM collected before day 3 may be falsely negative and should be repeated — see note below.
- If IgM is negative and was collected fewer than 72 hours after rash onset, repeat using serum collected ≥72 hours after rash onset.
- Any IgM serum specimens that are pre-approved by MDHHS to be sent to BOL must be frozen at < -20 ⁰C and shipped on dry ice to remain frozen during transport.
- Shipping to MDHHS BOL
- Ship overnight delivery. For weekend delivery, specify “Saturday Delivery” and apply a Saturday shipping label — without this, Friday samples arrive Monday and may be untestable.
- Pre-paid overnight and Saturday delivery labels available from BOL: mdhhslab@michigan.gov.
- Upper Peninsula providers: the Western Upper Peninsula Health Department Regional Public Health Laboratory (WUP Lab) can provide regional support for measles PCR testing. Contact your Regional Epidemiologist and MDHHS Division of Immunization at 517-335-8159 to arrange.
- If serum collection is not available in your office, collect the swab (and urine if indicated) for PCR and arrange for the patient to have serum drawn at the nearest laboratory. Call ahead to the receiving laboratory to inquire about their procedures for specimens from patients with potential airborne-transmitted infections — they may require a separate entrance or waiting area.
Interpreting results
- Negative PCR: does not rule out measles, especially if the swab was collected more than 3 days after rash onset. Consider clinical presentation and epidemiologic factors.
- Discordant results (e.g., negative PCR + positive IgM): evaluate clinical presentation, epidemiologic risk, and specimen timing. Contact your LHD or MDHHS.
- False-positive IgM: observed with rubella, roseola, herpesvirus, parvovirus B19, dengue, and elevated rheumatoid factor. Always attempt PCR in parallel.
- IgG serology: may be helpful in evaluating a suspect case but is not a substitute for PCR and is not sufficient to waive isolation after a known exposure. See Exposure Scenarios.
A positive PCR cannot distinguish vaccine strain from wild-type measles — both return as positive. Measles Virus Analysis (MeVA) genotyping is required to make this distinction: wild-type strains currently circulating in U.S. outbreaks are genotype D8 or B3; the vaccine strain (Edmonston lineage) is genotype A. MDHHS Bureau of Laboratories does not perform MeVA in-house but coordinates testing through the Wisconsin State Public Health Laboratory, with an average turnaround of approximately one week. Contact MDHHS Bureau Infectious Disease Prevention to initiate referral.
Until MeVA confirms a vaccine strain, the child must be managed as potentially infectious with wild-type measles and remain home in isolation. Advise parents that vaccine-related rash occurs in ~5% of MMR recipients (typically 7–12 days post-vaccination) and is a real possibility here — but cannot be assumed without laboratory confirmation in an outbreak context. Isolation is a precaution, not a diagnosis, and will be lifted promptly if MeVA returns genotype A.
PCR may be positive 6-45 days following MMR vaccination, with a median detection time of 11 days.
