This study, carried out to determine trends in measles cases and risk factors for measles in Bayelsa State found that the most reported age group were children less than 5 years, with the highest range between 1-4years, most studies allude the highest prevalence of measles in under-five year children.19 However, the analysis showed being less than five years as protective in this population and study period, this may be due to the small number of suspected cases reported over the period compared to the confirmed cases and the SIAs done during this period focusing on less than 5 years age group would have provided additional protection.
There was a preponderance of reported cases among males even though there is no known sex predilection as unvaccinated males and females are equally susceptible to infection by the measles virus.20 However, our findings are consistent with that of studies that observed male preponderance of cases.19,21 However a study in Zimbabwe reported a similar ratio of males to females.3
We noticed an all-year transmission of measles with two peaks in May and July in 2014,2015, 2017 and 2018 except in 2016 from May to August there were no reported cases due to health workers’ strike in the state. Similarly another study showed that measles cases were reported throughout the whole five-year period with no break in reporting, following similar patterns each year (from 2012 to 2016), though with a peak in number of reported cases in March.1 This is different from what was reported in a study in Abia State where most of the cases of measles occurred in the dry season, with the peak in January and February.9 However, it was recorded that measles transmission in Nigeria occurs through all months of the year, but peaks in the dry season (February, March and April).1
There was an increasing trend in the number of reported cases from 2014 to 2018 except in 2016 where a sharp decline was seen. This increase may be difficult to interpret as this may be attributed to either a low vaccination coverage or a strengthening surveillance system over the years. These options need to be explored. Further studies comparing vaccination coverage and surveillance activities during the period reviewed should explain this increase. Cases tend to start increasing at the end of the 3rd quarter of each year with a rise seen at the 4th quarter even in the 2019 forecast, this is expected as measles transmission is higher during hot seasons in Nigeria.1 This finding is similar to that of a 10-year study conducted in Makurdi, Nigeria, it was discovered that the cases of measles in the Federal Medical Center was higher from the last to the first quarter in each successive year.22
Only 9.35% of all reported measles cases were confirmed by laboratory diagnosis, this is quite low and is consistent with the findings in a similar study that found only 6.7% of measles cases in Nigeria over a five-year period were confirmed by laboratory testing.1 This shows that laboratory confirmation of measles is still very low in the state. All suspected measles cases are expected to be confirmed by laboratory testing by so doing outbreaks will be detected promptly. This will also enable documentation of decline in cases and progress towards measles elimination.2
The highest number of reported cases from Yenegoa LGA. may be attributable to the presence of a Federal Medical Centre in the LGA that serves as a referral center. In addition, being an urban area, the high population with overcrowding may predispose to measles infection. Measles being a highly contagious disease, recent contact and overcrowding are risk factors for disease transmission.21 Ekeremor, a rural area and Sagbama had the least reported cases within the same period, this is different from what was observed in a similar study in Abia State where about 75% of the measles cases occurred in rural areas.9 From this study, incidence rate was higher in urban areas and the odds of having measles was higher in those living in the urban areas than in the rural areas. A previous study revealed measles outbreak been less frequent in rural than in urban settings.23 Another study carried out in Bayelsa State on community participation and childhood immunization coverage found that the immunization status of children in the rural community was significantly better than those in the urban community studied.24 Implying that immunization in urban centers is inadequate.
Of the cases with data on vaccination status, 51.7% had not received any measles vaccine at all. This is not acceptable as free and effective measles vaccines were available in the state. From our study, people not vaccinated were more likely to have measles although this association was not statistically significant. Measles is vaccine-preventable and a child is eligible for measles vaccine once they attain nine months of age.2
There was good sample collection, storage and transportation practices in the state. Indicators of performance of the surveillance system such as timeliness of specimen reaching the laboratory within 3 days of specimen collection, was persistently low below the WHO recommended target of 80%.2 This delay in specimens reaching the laboratory could be a consequence of batching of specimens by the DSNOs for transportation to reference laboratories in Lagos where they are analyzed in order to save cost. This practice contributes to delay in confirmation of cases and outbreaks may be missed,
The proportion of feedback of serology results sent from the laboratory to the national level within 7 days of receipt of specimens was persistently low below the WHO recommended target of 80%,2 this is similar to findings in a study done in Zimbabwe.3 However, a general increase was noted in the period of 2015 and 2016, followed by a decline in 2017 and then an increase in 2018. Timely feedback from the laboratory is important for confirmation of cases and prompt decision making. This also helps to boost the morale of surveillance officers who contribute to the functioning of the system.
The data obtained for this study had some limitations that restrict conclusions drawn from its analysis, and thus may limit generalization of the findings. The information was derived from reported cases in the surveillance system so there may have been unreported cases, however this data set will contain most cases in the state as the data was gotten from surveillance sites where most cases are likely to report. Many variables had missing data for several cases such as number of vaccine doses received (67percent missing entries), date specimen was sent to the laboratory (4 percent missing entries) and date district received laboratory results (19 percent missing entries). Doubtful entries that produced 0 days for laboratory turn-around time and time interval between specimen collection and sent to the laboratory, these were excluded from the analysis. Mortality data was not collected and consequently case fatality rate could not be estimated. This is a pointer to gaps in data collection system in the state. Despite these limitations, this study was the first describing the measles trends in Bayelsa State and the accuracy of information on reported cases in the study depended on the accuracy of reports submitted and stored on the surveillance system. All available data over the study period was utilized.