Epidemiology of confirmed measles virus cases, surveillance, incidence, and associated factors in Eritrea: 18-year retrospective analysis

Abstract

Background: Despite the outstanding measles vaccine coverage (MVC) in Eritrea, sporadic outbreaks are not uncommon. Therefore, understanding the incidence of laboratory-confirmed measles virus cases, related factors, and spatial inequalities in testing and surveillance remains crucial. In this analysis, we evaluated the incidence and spatiotemporal distribution of measles in Eritrea. An evaluation of the factors associated with measles vaccination and IgM positive (+) febrile rash was also undertaken.

Methods: A retrospective (period: 2002-2020) study was carried out by abstracting data from the integrated disease surveillance and response database (IDSR). Data was analyzed using descriptive statistics and binary logistic regression. Spatial variability and distribution of confirmed cases was evaluated using ArcGIS Pro version 3.0.1.

Results: In total, 9,111 suspected cases, 2,767 [1,431 (51.7%) females] were serologically tested. The median (IQR) age, minimum-maximum age were 7 years (IQR: 4-14 years) and 1 month-97 years, respectively. Among the 608(21.9%) laboratory-confirmed cases, 534 (87.8%) were unvaccinated and 53 (9.92%) were < 1 year old. The crude incidence rate for MV was 14/100,000 persons. The age-specific positivity rate per 100,000 suspected cases tested was 21.5 with individuals >30 years presenting with the highest rates (69.9/100,000). Higher odds (OR) of MV test positivity was associated with age at onset - higher in the following age-bands [10-14 years: OR = 1.6 (95%CI, 1.1-2.2, value of p = 0.005); 15-29 years: OR = 7.0 (95%CI, 5.3-9.2, value of p = 0.005); and > =30 years: OR = 16.7 (95%CI, 11.7-24) p < 0.001]. Other associations included: Address - higher in Anseba (OR = 2.3, 95%CI: 1.7-3.1, value of p<0.001); Debub (OR = 2.7, 95%CI: 1.9-3.9, value of p < 0.001); Gash-Barka (OR = 15.4, 95%CI: 10.9-21.7, value of p < 0.001); Northern Red Sea (OR = 11.8, 95%CI: 8.5-16.2, value of p < 0.001); and Southern Red Sea (OR = 14.4, 95%CI: 8.2-25.2, value of p < 0.001). Further, test positivity was higher in health centers (OR = 2.5, 95%CI: 1.9-3.4, value of p < 0.001) and hospitals (OR = 6.8, 95%CI: 5.1-9.1, value of p < 0.001). Additional factors included vaccination status - higher in the unvaccinated (OR = 14.7, 95%CI: 11.4-19.1, value of p < 0.001); and year of onset of rash - (higher >2015: OR = 1.4, 95%CI: 1.1-1.7, value of p<0.001). Uptake of measles vaccine associated with a similar complement of factors.

Conclusion: In large part, efforts to eliminate measles in Eritrea are hindered by disparities in vaccine coverage, under-surveillance, and low vaccination rates in neighboring countries. Enhanced surveillance and regional micro planning targeting hard-to-reach areas can be an effective strategy to improve measles elimination efforts in Eritrea.

Keywords: epidemiology; measles; spatial inequality; surveillance; vaccination.