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Outbreak of Primary Infection of Mycobacterium Tuberculosis among Medical Students and Staff, King Saud University, Riyadh, 1997.


In October 1997, one patient who was working as an anatomy demonstrator at King Saud University, presented with cough, hemoptysis and acid fast bacilli (AFB) on a sputum smear. Initial screening found several other tuberculin infections. The Field Epidemiology Training Program was asked to help determine the source of infection, extent of the outbreak, and to suggest control measures to prevent further spread of the disease.


A list of all patients with positive sputum for AFB and positive culture for Mycobacterium tuberculosis for 1997 was obtained. The files of the patients with positive sputum for AFB were reviewed. All anatomy, catering staff, first- and second-year, and some of third- and fourth-year medical students were requested to be screened for Tuberculosis (TB). A second purified protein derivative (PPD) test was done for some of those with an initial negative PPD test. A case-control study for exposure of infected and uninfected medical students to common areas in the college was conducted.


AFB was detected in 4 medical students, 3 anatomy staff and 2 catering staff members. The only patient who had cavitary TB was from the catering staff. Among those who sought medical advice in King Khalid University Hospital during 1997, 65 patients had a positive culture for M. tuberculosis and another 26 patients had a positive sputum for AFB. Some of these patients were hospital- or medical-college related. Positivity rates of PPD tended to increase from 36.8% for the first-year medical students to 42.2% and 45.2% for the second- and third-year students respectively. However, fourth-year students had lower PPD positivity rates. Comparisons of PPD positivity rates by anatomy laboratory groups indicate most of the anatomy groups of students had high positivity rates. Similarly, PPD positivity rates were not associated with any individual anatomy demonstrator to be the source of infection. A bacille Calmette-Guerin (BCG) scar was present in 73.5% of the medical students. However, the percentage of a positive skin test among subjects with a negative BCG scar was 23.7%. Screening of the catering staff showed 34 (65%) out of 54 had a positive PPD. Recent infection was proved by an increase of 0.01 mm of PPD per day and positive conversion rate of 36.4%. The case-control study showed a high odds ratio due to exposure to mosque number 2. Moreover, the odds ratio gradually increased with increased frequency of praying in mosque 2. The next highest odds ratios were seen with the library, the dormitory and dormitory restaurant. The odds ratio increased with increasing exposure to the library but this trend was also not statistically significant. TB infection was not associated with the cafeteria where the patient with cavitary TB worked.


High infection and conversion rates should warn the health authorities of the seriousness of the problem and the possibility of these students developing active pulmonary TB. This outbreak can be used as evidence for the need of a skin test to all medical students and staff, at least at the time of entry to the medical college and periodically thereafter, since medical students, as any health care workers, are at risk more than others of getting the infection.