The spatial analysis of annual measles incidence and transition threat assessment in Iran in 2016

During the past years, due to the increase in immunization coverage and promotion of surveillance data, the incidence of measles decreased. This study aimed to determine the measles incidence risk, to conduct spatial mapping of annual measles incidence, and to assess the transition threat in different districts of Iran.

 A historical cohort study with retrospective data was conducted. The measles surveillance data containing 14 294 cases suspected of having measles in Iran were analyzed during 2014-2016. WHO Measles Programmatic Risk Assessment Tool was applied to calculate and map the incidence of measles in each district, to determine the annual incidence rate, and to conduct spatial threat assessment risk. Threat assessment was measured based on factors influencing the exposure and transmission of measles virus in the population. The annual measles incidence rate and spatial mapping of incidence in each Iranian district was conducted by Measles Programmatic Risk Assessment Tool. Data were analyzed by descriptive statistics in Excel 2013 and Arc GIS 10.3. 

Of 14 294 suspected cases, 0.6% (CI 95%: 0.599-0.619) were identified as clinically compatible measles, 0.280 (CI 95%: 0.275-0.284) as confirmed rubella, 0.52% (CI 95%: 0.516-0.533) as epi-linked measles, 4.6% (CI 95%: 0.450-0.464) as lab-confirmed measles, and 94% (CI 95%: 93.93-94.11) were discarded. The annual incidence rate in cases per 100 000 populations increased from 0.0726, (CI 95%; 0.0714-0.0738) in 2014 to 0.1154 (CI 95%; 0.1135-0.1173) in 2016, and the 3-year incidence rate during the study period was 1.032 (CI 95%; 1.017-1.047) and the annual average was 0.3442 (CI 95%; 0.3387-0.3496).

 The average annual incidence rate of measles in Iran was low, but after a 11-fold increase in the number of measles cases in 2015, the number of measles cases decreased to more than 7-times in 2016. However, maintaning a high immunization coverage of measles and timely vaccination can be effective in reaching the goal of measles elimination.