Incidence of Coagulase-positive Staphylococci in the Upper Respiratory Tract of Dental Students and a Study of Their Transmission during a Routine Dental Prophylaxis

¹ School of Dentistry, University of Maryland, Baltimore, Maryland

The investigation of the incidence and transfer of pathogenic S. aureus has been continued.² The experiments reported here were conducted on two classes of dental students during a period of 1 year. One class (Class A) was swabbed both years, i.e., at the beginning of their clinical training and 1 year later. The other class (Class B) was swabbed only at the beginning of their clinical training.

The following general conclusions were made from this study: (1) a carrier tended to harbor only one phage pattern organism at a time; (2) the nasal cavity appeared to have been the main reservoir of the phage-typable staphylococci in an asymptomatic carrier; and (3) the persistent type of carrier tended to remain persistent with the same phage pattern.

The incidence of coagulase-positive carriers was 65-88 per cent. However, compared with results of previous studies on dental students, the incidence in both classes was somewhat high. The difference in incidence was explained partially by a difference in the definition of staphylococcal pathogens. Two other factors that may have accounted for the variation in results were the number of different swabs taken from each subject and the areas swabbed. From these results, it was found that from 3-13 per cent of the carriers would have been missed if only one rather than three swabs on different occasions had been obtained and that from 13-19 per cent of the coagulase-positive carriers would have been missed if only nasal swabbings had been used instead of nose, throat, and mouth swabbings.

Statistical analysis of all the results was included. An analysis of one class indicated there was no significant increase in the carrier rate from the beginning of their Junior year (first clinical year) to the beginning of their Senior year. Approximately 50 per cent, however, changed their status from carrier to non-carrier or from non-carrier to carrier. The other 50 per cent remained either carrier or non-carrier.

One group of students, who were known carriers of coagulase-positive staphylococci, represented the dentist, while students known not to be carrying coagulase-positive organisms represented the patient. Each experiment consisted of the carrier-dentist performing a routine prophylaxis on the non-carrier patient, lasting an average of 34 minutes. With the use of swab techniques, attempts were made to isolate from the patient organisms known to have been harbored by the dentist. Air samplers were used to determine whether the dentist liberated his organisms into the environment of the dental chair.

In 19 experiments using healthy normal dental students who were asymptomatic nose, throat, or mouth carriers, no direct or indirect transfer of pathogenic staphylococci to negative students was demonstrated. Two experiments in which organisms were carried on clothing, as well as on other areas, showed evidence of a transfer to the air, thus supporting the views of other investigators that a clothing carrier has a greater chance of transmitting his organism. No conclusions could be made regarding transmission by symptomatic carriers, since satisfactory subjects were not available.

The Fort Detrick slit samplers used were very satisfactory for obtaining air samples. They were simple to handle and required a minimum of laboratory time, and the experimental time could be correlated easily with the impinging time. Of the 10 carrier-dentists used, 3 had organisms resistant to penicillin, as determined by the paper-disk method. Most of the organisms were sensitive to the other 15 antibiotics used.

This article has been cited by other articles:

				H. T. Knighton Coagulase-positive Staphylococci in Oral and Nasal Areas of Dental Students: A Four-Year Study Journal of Dental Research, May 1, 1965; 44(3): 467 - 470. [PDF]