Diphtheria, pertussis, and tetanus serosurvey in Saudi children.

OBJECTIVE: To evaluate immune protection against vaccine-preventable diseases targeted by the Expanded Program of Immunization in Saudi Arabia. METHODS: The study was carried out from September 2001 to February 2002. Using multistage sampling techniques, samples were collected from 5 regions of Saudi Arabia and sent for laboratory assay from the following age groups; 50 samples at 12 months, 50 at 6 years, and 100 at 17 years. Sera were assayed for diphtheria, tetanus, and pertussis. Sero neutralization was used for anti-diphtheria antibody assay, while enzyme linked immunoassay was used for anti-tetanus, anti-filament hemoagglutination (anti-FHA), and anti-pertussis titer (anti-PT) antibody assay. RESULTS: This survey showed that 100% of children had protection levels (>/=0.01 IU/ml) against diphtheria at one year, 100% at 6 years, and 93.7% at 17 years. For tetanus, 95.9% had protection levels (>/=0.1 IU/ml) at one year, 100% at 6 years, and 98.9% at 17 years. The geometric mean titer (GMT) of anti-FHA is 22 at one year, 29 at 6 years, and 24 IU/ml at 17 years, while the GMT of anti-PT is 36 at one year, 18 at 6 years, and 11 IU/ml at 17 years. CONCLUSION: Children at one, 6, and 17 years are well protected against diphtheria, pertussis, and tetanus.

Serosurvey of measles, mumps and rubella antibodies in Saudi children.

OBJECTIVE: A serosurvey study to evaluate the proportion of children with antibodies against diseases targeted by the Expanded Program of Immunization in the Kingdom of Saudi Arabia. METHODS: Using multistage sampling techniques, we collected samples and sent them for laboratory assay from the following age groups; 100 samples at 6 months, 12 months, 18 months, 6 years, 13 years, and 17 years. We conducted the study from September 2001 to February 2002. We assayed sera for measles, rubella, and mumps antibodies in the measles-mumps-rubella reference laboratory in Germany, using enzyme immunoassay and plaque neutralization (PN) as a backup test for equivocal and negative samples. We only carried out a backup test for measles samples. RESULTS: The age group of 6 months had the highest proportion with negative measles antibodies. After adding the backup test (PN), the proportions of children with protective measles antibody were; 64% at 6 months, 87% at 12 months, 91% at 18 months, 75% at 6 years, 96% at 13 years, and 98% at 17 years. Rubella antibody positivity rates (>7 IU) were 28% at 6 months, 49% at 12 months, 97% at 18 months, 98% at 6 years, and 100% at 13 years. While positivity rates in mumps were 14% at 6 months, 29% at 12 months, 59% at 18 months, 64% at 6 years, and 75% at 13 years. CONCLUSION: The unexpected low proportion of children with protective level at 6 years, despite being vaccinated with 2 measle doses is an important phenomenon. This reflects the interference between the first and the second measles dose. The Ministry of Health decided to conduct a catch up campaign targeting 1st through 3rd grade primary schools, who did not catch the mass campaign conducted in 2000. Also, this supports the decision taken by the ministry to change the measles immunization schedule to MMR at 12 months and a second dose at 6 years of age.

Changes in epidemiological pattern of Meningococcal disease in Saudi Arabia. Does it constitute a new challenge for prevention and control?

OBJECTIVE: Meningococcal meningitis epidemics, which occurred in the Kingdom of Saudi Arabia (KSA) coincided with Hajj and Umra seasons; the 2 major pilgrims to Muslims. In many countries, the disease showed major changes of its epidemiological determinants, in particular to age and prevailing serogroup. This study was conducted to determine the epidemiological trend of meningococcal meningitis disease in KSA. METHODS: All confirmed meningococcal meningitis cases reported in KSA during the period from January 1999 to December 2002 were studied retrospectively. Confirmation of cases was based on isolation of the causative organism from cerebrospinal fluid (CSF) or blood culture or detection of antigen in the CSF. Personal, clinical and laboratory results were analyzed using Epi info version 6 software. Categorical data were tested using chi2 test. RESULTS: A total of 729 cases were reported, 304 cases (42%) were among people coming from abroad for Hajj or Umra and 425 (58%) were among local population. Nearly half of the later (48%) were reported at the 2 holy areas of Makkah and Madinah, KSA. Thirty-nine percent of cases were children aged <2 years and 58% were <5 years of age. Proportion of cases affected with serogroup W135 increased over time (up to 95%) and significantly affected children aged <5 years (p<0.001). CONCLUSION: Continuous monitoring of epidemiological determinants is essential to guide vaccination policy.