This study describes 33 laboratory-confirmed cases
of measles that occurred in Norway in 2011, mainly
among unvaccinated children between seven months
and 10 years of age. Laboratory testing included
detection of anti-measles IgM- and IgG antibodies
by enzyme-linked immunosorbent assay (ELISA) and
molecular detection and characterisation of measles
virus by polymerase chain reaction (PCR) and sequencing.
Epidemiological data and genotyping revealed
that the measles cases originated from eight separate
importations, resulting in four outbreaks and four
sporadic cases. Except for the first outbreak which
affected 18 cases, limited secondary spread occurred
in each of the three other outbreaks. The outbreaks
were caused by measles virus genotypes B3, D4 and
D9, whereas genotypes D8 and B3 were detected in
the sporadic cases. This study highlights that genetic
characterisation of measles virus is an essential tool
in the laboratory surveillance of measles, especially
in countries like Norway which are approaching the
measles elimination goal. The investigation revealed
that importation of measles resulted in subsequent
transmission within Norway to non-vaccinated individuals,
and twelve cases occurred in healthcare settings,
involving both staff and children. The four cases
detected among healthcare workers (HCWs) emphasised
that the coverage of measles-mumps-rubella
(MMR) vaccination among healthcare personnel needs
to be improved and both primary and secondary vaccine
failure was demonstrated in two fully immunised
HCWs.
Introduction
Measles, a highly contagious respirat