On 8/3/2003 the General Health Directorate of Al-Madinah region reported an unusual increase in measles cases. The Field Epidemiology Training Program was assigned to investigate this outbreak and recommend control measures. On reaching Al-Madinah the team visited the Regional Health Directorate, the supervisor sectors, Hospitals and Health Care Centers. At the health centers, the team interviewed the Directors of the centers and Health staff and reviewed patient records. The team also visited the school health units for boys and girls and one of the schools were suspected measles cases had appeared, in order to develop a framework for further investigation.
It was decided to conduct a case control study to identify risk factors associated with the occurrence of this outbreak. A Measles case was defined according to clinical surveillance case definition of suspicious and confirmed cases. A questionnaire was prepared and distributed to all Hospitals, Primary Health Care Centers (PHCCs), and school Health Units to be filled for all measles cases; whether suspected or confirmed, old or new. All cases that met the case definition and had complete residential addresses were enrolled in the study. One control from the same family or neighborhood was selected for each case.
During the period from January first to June 15th 2003, 355 cases of clinically diagnosed measles were reported, giving an attack rate of 24/100,000 persons.
Figure 1 demonstrates the epidemic curve of this outbreak. Table 1 demonstrates the demographic characteristics of cases and control. The highest age group affected was children aged 5-14 years, 171 (48.2%). Saudi nationals accounted for 297 cases (83.7%). Females constituted 53.5% and students accounted for 145 (43.7%), 110 (33%) of them were from primary schools. The mean family size of measles cases was 8 members (median 7). Most of the cases (88.3%) were the only affected family member, 10% were from families with two affected members and 1.7% were from families with three affected members.
All cases had fever followed by rash for a median duration of three days (range 2-14 days), runny nose (62%), conjunctivitis (60%) and koplik spots (48%). Ninety eight percent of cases had presented to governmental health facilities; 31% of who were admitted into hospital for a median duration of three days (range 1-8 days). Over two thirds (69%) of blood samples were serologically confirmed (IgM).
There were 112 (32.5%) cases who had history of contact with confirmed measles cases. Schools were the major location for contact with measles infection.
The risk of measles infection was higher among non-vaccinated individuals (OR 2.33, 1.62<OR<3.35). History of measles vaccination was significantly lower among cases (57.3%) compared to controls (75%) (OR 0.45, 95% CI 0.32<OR<0.63). Among Saudis, 175 (61.0%) cases had been previously immunized compared to 228 (81.1%) controls (OR 0.36, CI 0.24<OR<0.54). Among non-Saudis 23 (28.4%) cases had been previously immunized compared to 26 (44.8%) controls (OR 0.49, CI 0.23<OR<1 .05).
History of receiving two dose or more of measles containing vaccine was lower among cases (OR 0.43, CI 0.30-0.62), in addition to possessing a birth certificate (OR 0.47, CI 0.300.73).
Editorial note:
This sporadic outbreak of measles is attributed to the accumulation of susceptible individuals. In this study, the majority of cases (48.2%) were in the 5-14 year age group, which is consistent with previous studies. Kamel et al. reported that 68.1% of measles cases in Saudi Arabia occurred among the 5-15 years age group.[1] 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.[2]
Infants below one year (18.6%) are too young to be immunized, their source of infection could have been school-aged infected siblings or infected mothers. Young adults aged 15 to 25 may be susceptible because of their lower vaccination coverage at the start of the immunization program. They may have been too old for immunization, may have received a vaccine of low potency, or may have escaped measles infection during childhood due to a general decline in incidence rate in the community.[3] It has been 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.[4]
The fact that 57.4% of measles cases occurred in immunized individuals is consistent with previous studies.[5] It was also found that 20% of immunized cases had received a single dose of measles vaccine. Repeated experience has shown that a two-dose regimen of measles vaccine is required to eliminate measles. Pebody et al. reported that 2-4 years after receiving a first dose of MMR vaccine at 12-18 months, 19.5% of pre-school children got measles.[6]
School-aged children comprised the majority of cases in this study, and may have acted as an important source of infection for younger siblings. Contact between households during Eid holiday in a suitable climate may also have been responsible for the increase in cases following that holiday.
It was recommended to aim for an immunization coverage against measles of at least 95% in each successive cohort. Health education messages should be directed to mothers to promote vaccine-seeking behavior. The adult population should be considered for measles vaccination as they be-come at risk to develop the disease.
A Measles vaccination campaign should be conducted every 3-5 years aiming to cover all children regardless of prior disease or immunization status. 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 J Ped 1989,3(4):5452.
- Global program for vaccines and immunization. Immunization policy. Geneva, WHO, 1995 (WHO/EPI/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, EI-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 HIth 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 Page 21
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Table 1: demographic characteristics of cases and controls, measles outbreak, Al-Madinah region 2003.
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Cases
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Controls
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No.
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%
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No.
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%
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|
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Age Group
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< 1 year
|
66
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18.6
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6
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1.7
|
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years 1-4
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48
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13.5
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111
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31.5
|
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5-14 years
|
171
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48.2
|
146
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41.5
|
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15-24 years
|
32
|
9
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33
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9.4
|
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25-44 years
|
35
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9.86
|
43
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12.2
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>=45
|
3
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0.84
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13
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3.7
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|
Gender
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Male
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165
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46.5
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188
|
53
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|
Female
|
190
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53.3
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167
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47
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Nationality
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Saudi
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297
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83.7
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297
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83.7
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Non-Saudi
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58
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16.3
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58
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16.3
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Occupation
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Students
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145
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43.7
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103
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31.8
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Pre-school Children
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125
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37.7
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151
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46.7
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Housewives
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33
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9.9
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22
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6.8
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Employees
|
12
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3.6
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20
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6.2
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Non-Employed
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12
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3.6
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12
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3.7
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Self-Employed
|
5
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1.5
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8
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2.4
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Laborer
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0
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0.
|
8
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2.4
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Previous Measles Vaccine
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||||
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Yes
|
198
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57.4
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254
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74.9
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No
|
147
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42.6
|
85
|
25.1
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