On 2/12/2006, the General Health Directorate of Jazan region reported an unusual increase in measles cases. The Field Epidemiology Training Program (FETP) was assigned to investigate this outbreak and recommend control measures.
A descriptive study followed by a case-control study was carried out. The descriptive study covered all the cases of measles that occurred from April 1 to December 31,2006 in Jazan region. The case-control study covered Al Ardha and Baish areas in Jazan where most of the measles cases had occurred.
A measles case was defined according to clinical surveillance case definition of suspicious and confirmed cases. A questionnaire was prepared and filled by direct interview and by reviewing all related records. All cases that met the case definition and had positive serologic test for IgM were enrolled in the descriptive study; 110 of these cases from Alardha and baish sectors were enrolled in the case-control study. One control from the same family or neighborhood was selected for each case, during the study period.
During that time period, 347 cases of clinically diagnosed measles were reported in Jazan region, out of which 265 cases were confirmed serologically.
Among the confirmed cases 158 were from Al Ardha sector and 41 from Baish sector. Figure 1 demonstrates the monthly trend of this measles outbreak, as compared to the previous 2 years.
Females constituted 58.6% and 83% from rural areas. Only 4.9% of cases were below 6 months of age, 12.9% were 6-8 months of age, 19.6% cases were 9-11 months of age and another 9.1% were at age 12 months i.e. put together 46.6% of cases were in the age group where they are not likely to be immunized under the current immunization schedule for Measles. Another 14.8% cases were in the 1-5 year age group i.e. age not yet entitled for 2nd dose of MMR at school entry; 11.0% of cases were in the 6 to 15 year age group, which are expected to have received two doses of measles vaccine; 27.7% were older than 15 years. Among the 99 cases up to 12 months of age only 1 was vaccinated and among 21 cases of 12 months age only 3 (12.5%) were vaccinated. Among children 1-5 years of age 86.2% were vaccinated, among those 6-15 years of age 37.5% were vaccinated, and among cases over 15 years only 5.5% were vaccinated.
Regarding the case-control study, among cases, 26.4% had been previously immunized, as compared to 36.4% of controls (OR 0.637, 95% CI 0.3531.114). Among children 1-4 years of age 94.7% were vaccinated compared to 95.8% of controls. Among those 1524 years of age 13.3% were vaccinated compared to 14.3% of controls. Among the measles cases 91.1% gave history of visiting hospital/PHC since April 2006 compared to 60% controls (OR 6.833; 95% CI 2.951-15.822).
Among the measles cases 99 (92.5%) gave history of visiting hospital/PHC within the 3 weeks before onset of the disease compared to 54 (60%) controls with OR of 8.250 (95% CI 3.580-19.010) which exhibited a statistically significant relationship.
Among the measles cases 52.6% gave history of contact with a measles case since April 2006 as compared to 63.6% controls (OR 0.633, 95% CI 0.340-1.179).
Regarding nutritional status 89.7% among the measles cases were normal as compared to 90.9% of controls (OR 0.871; 9 CI .277-2.744).
Editorial note:
In this outbreak, a total of 347 confirmed cases of Measles were reported until December 31, 2006. Based on the review of the data since 1995, the pattern shows that the number of confirmed cases reported is clearly in excess of normal occurrence of Measles cases in the region and should be considered of epidemic nature.
In year 2002, EPI vaccination schedule of one dose of Measles vaccine at age of 6 months followed by a dose of MMR vaccine at age of 15 months was replaced with first dose of MMR at age of 1 year followed by a second dose at school entry. Since the change in schedule, this is the second outbreak in the region in the last 3 years. However as compared to the February to April peak in 2004, this year the disease is apparently having the same level of presence since its beginning in May.
Kamel et al [1] reported that 68.1% of the reported cases of measles in Saudi Arabia were among the age group of 5 years to less than 15 years. Another study conducted in Alexandria, Egypt [2] reported that 69.1% of measles cases were seen in the 5 to under 15 years age group.
The shift in age distribution of measles cases towards older children is one of the major effects of immunization programs on measles epidemiology due to the lowering of exposure rate in the community.[3] Young adults aged 15 to 24 in this outbreak (13.6%) might have been susceptible because of their lower vaccination coverage at the start of the immunization program, when they could have been too old for immunization or they might have received a vaccine of low potency and less heat stability, or they might have escaped measles infection during childhood due to a general decline in incidence rate in the community.[4,5]
It is recognized that a substantial number of individuals are now entering their adult life without having encountered the measles virus either in its wild or vaccine forms.[6] We found that 29 (26.4%) cases of measles occurred in immunized individuals, which is lower than in a study conducted in Alexandria, Egypt reporting that the majority of measles cases have histories of measles vaccination (79.4%).[2]
The large number of cases of measles occurring in immunized individuals is related to the level of coverage achieved. It is known that as immunization coverage increases, a higher proportion of cases will occur among immunized children.[1]
It was recommended to immunize children between 6-12 months of age to control this outbreak, in addition to strengthening routine vaccination at 1 year of age. Health education messages should be directed to mothers to promote vaccine-seeking behavior. In addition to the MMR measles containing vaccine given at 12 months and at school entry (4-6 years), the adult population should be considered for measles vaccination as they become at risk to develop the disease. Follow up studies should be conducted to update the epidemiological and immunological situation of measles, particularly in response to higher vaccination coverage.
References
- Kamel MI et al. Comparison of some epidemiological characteristics of vaccinated and unvaccinated measles cases in Saudi Arabia. Alex JPed 1989,3(4):5452.
- Global program for vaccines and immunization. Immunization policy. Geneva, WHO, 1995 (WHO/EPF GEN/95.3).
- Frank JA et al. Major impediments to measles elimination: the modern epidemiology of an ancient disease. Am J dis child 1985,139:881-7
- Hasab A. Impact of measles vaccination program in Kuwait. Bull High Inst Pub Hlth, 1987,17(3): 1-8
- Tayil SE, El-Shazly MK, El-Amrawy SM, Ghouneim FM, Abou Khatwa SA, Masoud GM. Sero-epidemiological study of measles after 15 years of compulsory vaccination in Alexandria, Egypt. Eastern Med Hlth J 1994,4(3):
- Pebody RG. Immunogenicity of second dose Measles-Mumps-Rubella (MMR) vaccine and implications for serosurveillance. Vaccine 2002, 20(7,8): 1134-114.
