Measles and rubella in Norway
The last nationwide measles epidemic in Norway was in 1983 – 84 (3). In 2010 and 2012 – 15 the reported incidence rate in MSIS was consistent with the WHO's elimination indicator. However, a relatively large outbreak took place in 2011, with slightly more than six cases per 1 000 000 (4).
The last reported major rubella outbreak in Norway was in 1978 – 79. A smaller local outbreak occurred in 1995 – 96. Since 1999, the incidence rate for rubella has corresponded to the elimination indicator, and the last reported case of congenital rubella syndrome following rubella infection in Norway was in 1990 (1).
However, the Norwegian Institute of Public Health has data indicating that general practitioners use diagnostic codes for measles and rubella more frequently than is suggested by the number of cases notified to MSIS. Only around half of the reimbursement codes recorded are followed by a code for laboratory tests (Inger Cappelen, Norwegian Institute of Public Health, personal communication). This may indicate that Norwegian doctors do not follow the recommendation in the Guidelines for infectious disease control to follow up suspicion of measles or rubella with microbiological testing.
The Norwegian surveillance system for measles and rubella is a passive case finding that depends on healthcare personnel and laboratories reporting cases. Compared to an active system in which the public authority contacts all actors possessing information, this may have contributed to underreporting and delayed notifications of these diseases in Norway.
When few cases are reported, it is difficult to know whether there are in fact few cases of disease, whether there are cases that have not been reported, or whether there are patients who have not been tested. The reports sent to WHO should therefore provide information on the number of suspected cases tested (at least two per 100 000 inhabitants). For the years 2014 and 2015, the test rate for measles in Norway was lower than recommended – 0.78 and 1.18 per 100 000 for measles and 1.0 and 0.76 per 100 000 for rubella, respectively.
Nevertheless, most reported cases in Norway are confirmed by laboratories, and all samples sent to the Norwegian Institute of Public Health are examined in a WHO-accredited laboratory. The proportion of suspected cases of disease in which retrieval of relevant information is initiated within 48 hours from the time of notification is, however, unknown (WHO indicator for disease investigation, target at least 80 % of cases). Examples of relevant information are date of onset of the rash, date of microbiological sample collection and information on previous vaccinations.
The Norwegian Institute of Public Health assumes that few clinicians notify the diseases before the diagnosis has been verified virologically and this target is therefore not achieved. Very few cases are notified by telephone to MSIS. In Norway, an unknown place of infection is only exceptionally reported, and no known cases are attributed to the virus being endemic within the country. This indicates that we have a good overview of the sources and spread of infection.