Communicable Diseases Network Australia (CDNA)

Pathology laboratory diagnosis of measles

This document prepared by the Public Health Laboratory Network provides information on the laboratory diagnoses of measles.

Serology

Measles-specific IgM antibody is the mainstay of the diagnosis of acute measles. An IgM response will be present in approximately 75% of patients 3 days after rash onset, rising to approach 100% after 7 days. A measles IgG antibody test should preferably be performed together with the IgM assay to aid interpretation.

A 5 mL tube of clotted blood is the preferred specimen for serological testing.

When no measles IgM or IgG antibody is detected in a sample collected within 3 days of rash onset from a case of clinical measles, repeat testing is recommended after 7 days.

Direct detection

Virus can be detected in the respiratory tract for up to 3 weeks after rash onset using polymerase chain reaction (PCR). It is detectable for a shorter time by immunofluorescence and culture (one to two days). Measles virus can also be detected in peripheral blood and early catch urine.

Recommended samples

1. Nasopharyngeal aspirates or nasopharyngeal swabs are the preferred sample for antigen detection by immunofluorescence, nucleic acid detection by PCR, and culture. Otherwise throat swabs or nasal washes should be sent for culture and PCR, but are less suitable for the antigen detection tests. A dry¹ sterile swab of the nasal passage combined with a similar swab from the back of the throat is the recommended specimen for detection of viral nucleic acid (PCR). Swabs should be cotton, rayon or dacron-tipped, plastic-coated or aluminium shafted swabs. They should be placed into viral transport medium. Samples should be stored and transported at 4° C. If arrival at the testing laboratory will be delayed more than 72 hours then, if possible samples should be frozen at –70° C and transported on dry ice. Do not freeze at –20° C.

2. Early catch urine should be stored and transported as for swabs.
3. Heparinised blood for PCR should preferably be stored and transported at room temperature.
4. Clotted blood is suitable for serology.

Guidelines

1. Patients seen within 1 week of onset of rash should have samples for direct detection plus culture and clotted blood for serology collected.

2. Patients seen between 1 week and 3 weeks after the onset of rash should have clotted blood collected for serology and a respiratory sample for PCR.
3. Patients seen more than 3 weeks after onset of rash should only have clotted blood collected for serology.
4. Testing of asymptomatic contacts may be undertaken, but the reliability of serological and direct detection tests in that situation is not known and cannot be relied on to exclude incubating measles infection.

Further Advice

Advice can be sought from your pathology practice’s Clinical Microbiologist and/or your local Public Health Laboratory. The Public Health Laboratory Network (PHLN) members can be identified from http://www.health.gov.au/phln

Not a swab pack with its own bacterial transport medium.