Laboratory confirmation of measles in elimination settings: experience from the Republic of the Marshall Islands, 2003.
OBJECTIVE
To highlight the complications involved in interpreting laboratory tests of measles immunoglobulin M (IgM) for confirmation of infection during a measles outbreak in a highly vaccinated population after conducting a mass immunization campaign as a control measure.


METHODS
This case study was undertaken in the Republic of the Marshall Islands during a measles outbreak in 2003, when response immunization was conducted. A measles case was defined as fever and rash and one or more of cough, coryza or conjunctivitis. Between 13 July and 7 November 2003, serum samples were obtained from suspected measles cases for serologic testing and nasopharyngeal swabs were taken for viral isolation by reverse transcriptase polymerase chain reaction (RT-PCR).


RESULTS
Specimens were collected from 201 suspected measles cases (19% of total): of the ones that satisfied the clinical case definition, 45% were IgM positive (IgM+) and, of these, 24% had received measles vaccination within the previous 45 days (up to 45 days after vaccination an IgM+ result could be due to either vaccination or wild-type measles infection). The proportion of IgM+ results varied with clinical presentation, the timing of specimen collection and vaccination status. Positive results on RT-PCR occurred in specimens from eight IgM-negative and four IgM+ individuals who had recently been vaccinated.


CONCLUSIONS
During measles outbreaks, limiting IgM testing to individuals who meet the clinical case definition and have not been recently vaccinated allows for measles to be confirmed while conserving resources.
Hyde
Terri B
TB
Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, GA, United States of America. thyde@cdc.gov
Nandy
Robin
R
Hickman
Carole J
CJ
Langidrik
Justina R
JR
Strebel
Peter M
PM
Papania
Mark J
MJ
Seward
Jane F
JF
Bellini
William J
WJ
D019411:Clinical Laboratory Techniques; D004196:Disease Outbreaks; D006801:Humans; D017589:Immunization Programs; D007075:Immunoglobulin M / Q000276:immunology; D008457:Measles / Q000453:epidemiology* / Q000276:immunology / Q000517:prevention & control*; D008458:Measles Vaccine / Q000008:administration & dosage* / Q000276:immunology; D008849:Micronesia / Q000453:epidemiology; D011159:Population Surveillance; D020133:Reverse Transcriptase Polymerase Chain Reaction
D007075:Immunoglobulin M; D008458:Measles Vaccine