Ibrahim O. Al-Orainey

Nationwide community survey of tuberculosis epidemiology in Saudi Arabia

In the first nationwide community-based survey of the epidemiology of tuberculosis in Saudi Arabia, 7721 subjects were screened in the 5 provinces (using an equal proportional allocation formula) for 2 parameters: (1) prevalence of positive Mantoux test in non BCG vaccinated subjects; (2) prevalence of bacillary cases on sputum culture. The prevalence of positive Mantoux reaction in children aged 5-14 years was 6% +/- 1.8; higher in urban areas (10%), and lower in rural areas (2%), thus classifying Saudi Arabia among the middle prevalence countries. These relatively good results (by Third World standards) could reflect the rise of the standard of living and wide availability of free treatment for active cases with a lowered risk of infection in the community. This view is supported by the fact that in our survey, only one subject grew Mycobacterium tuberculosis in the sputum. However, there were foci of high prevalence of Mantoux reaction in the urban communities in the Western province (20% +/- 8.7 urban; 1% +/- 1.9 rural). The problem may be caused by the fact that the province receives every year over a million pilgrims, some of whom are known to settle illegally and escape the usual screening for tuberculosis imposed on foreign labourers. In conclusion, even in the absence of an enforceable national programme for the eradication of tuberculosis, the economic standard and wide availability of free treatment for active cases has resulted in relatively low rates of prevalence of tuberculin sensitivity in children. The foci of high prevalence in the Western Province require special screening arrangements.

Diagnosis of latent tuberculosis: Can we do better?

Latent tuberculosis infection (LTBI) is often diagnosed by the tuberculin skin test (TST). The latter has several limitations with regard to its sensitivity and specificity. It may be positive in people with prior bacille Calmette-Guérin (BCG) vaccination or exposure to nontuberculous mycobacteria. False negative TST results frequently occur in patients with impaired T-cell function. Therefore TST results have to be interpreted taking into consideration the pretest risk of TB infection or reactivation. Recently, interferon gamma release assays (IGRA) were introduced for the diagnosis of LTBI. These include the T-SPOT-TB and the QuantiFERON®-TB Gold tests.These tests measure interferon gamma released in response to T-cell stimulation by specific Mycobacterium tuberculosis antigens. These tests have been shown to be more specific than the TST as they are not affected by BCG vaccination. Their sensitivity was similar to that of the TST and in some studies they correlated better with the degree of exposure. In immune-compromised patients their sensitivity was better than that of the TST. IGRA tests were shown to have better predictive value for the development of active disease among individuals with LTBI. These tests are expensive. Their most cost-effective utilization is as confirmatory tests in patients with positive TST results, particularly in areas with high rates of BCG vaccination.

Tuberculosis incidence trends in Saudi Arabia over 20 years: 1991-2010.

OBJECTIVE: To evaluate tuberculosis (TB) incidence rates and trends over a period of 20 years (1991-2010) and assess the impact of the National TB Control Program (NTP) on incidence trends. METHODS: This is a retrospective study of TB surveillance data reported by the Ministry of Health. We evaluated TB incidence data by nationality, age, and region of the country and assessed incidence trends over 20 years of study. Chi-squared test was used to assess trend change and its significance. RESULTS: There were a total of 64,345 reported TB cases over the study period. Of these 48% were Non-Saudis. TB annual incidence rate ranged between 14 and 17/100,000. For Saudis, the rate ranged between 8.6 and 12.2/100,000. Non-Saudis had 2-3 times higher incidence. Disease trend was rising over the first 10 years of the study period then it started to fall slightly. The incidence increased with age, but only people older than 45 years showed a declining trend. Regional variations were observed. Makkah and Jazan regions had the highest incidence rates. Disease trends were rising over the last 10 years in Makkah and Central regions. CONCLUSION: TB control seems to be facing some challenges in several regions of the Kingdom. NTP needs to evaluate and improve TB control strategies in order to reduce disease incidence to elimination levels.