Risk of Bacterial Transmission in Dental Practice

Michael John, MB, Ch.B., FRCP(C) •

J Can Dent Assoc 2000; 66:550, 552

Every day, bacteria and viruses are passed between people at home, in the workplace and in the community. Given the number of these organisms found in the mouth and nasopharynx and the potential for aerosolization of blood and saliva during dental procedures, it is likely that transmission occurs frequently in this setting. Although few studies have looked at transmission of bacteria in dental practice, indirect evidence that this occurs can be obtained from seroprevalence studies that show that antibodies to a number of viruses found in saliva (such as cytomegalovirus [CMV], influenza virus and respiratory syncytial virus [RSV]) are more common in dentists than in the general population and increase with time from graduation.1 Carriers of bacteria may be asymptomatic, and transmission to the dental worker and patients can occur if infection control measures, such as use of gloves, masks, protective eye wear and hand hygiene practices are not adhered to.

Bacteria that May Be Transmitted in the Dental Office


Mycobacterium tuberculosis, the cause of tuberculosis, is one of the few diseases that is spread via the airborne route. Aerosolized bacteria may remain suspended in the air for long periods of time and inhaled into the lungs of a susceptible person. There have been reports of transmission of tuberculosis in the dental setting.2,3 Because masks worn in dental offices are not considered adequate to prevent transmission of tuberculosis, it is important to identify patients at high risk. Patients who are suspected of having tuberculosis should be referred to an appropriate physician for diagnosis and treatment before receiving dental treatment. If emergency dental treatment is necessary for patients with active tuberculosis, they should be referred to a specialized facility with negative pressure and adequate air exchanges. If this is not possible, expert advice should be obtained. In Canada, patients at higher risk are aboriginal people, people from areas of high prevalence, people infected with HIV, the poor and homeless and drug abusers. Clinical signs that may suggest tuberculosis include chronic cough, fever and weight loss.

Staphylococcus aureus

S. aureus, including methicillin-resistant S. aureus (MRSA), is one of the most common causes of both community-acquired and hospital-acquired infections. Recently, strains of these bacteria that are resistant to most antibiotics have become a problem in Canada, particularly in Ontario. These strains are no longer confined to hospitals: Shahin and others4 reported spread of this organism to a number of children in a Toronto daycare. Reports of community-acquired cases have also come from the United States.5 The nose and mouth are the natural habitat of S. aureus, and carriage on dentures has been reported.6 Dental workers who become nasally colonized with MRSA may transmit the organism to patients through shedding from their noses or via their hands if infection control practices are inadequate.

Other Bacteria

A number of bacteria may be found in the mouth and throat of people who show no symptoms. Asymptomatic carriers can transmit these bacteria to susceptible people in whom infection can occur. The route of transmission is via droplet spread, which can be prevented by wearing a mask and washing or disinfecting hands. During the winter months, 10 to 20% of all people may be asymptomatic carriers. Bacteria that can be spread in this way include: group A streptococci, Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis, Corynebacterium diphtheriae and Bordetella pertusis. These bacteria can cause a wide range of illnesses from pneumonia, to “strep throat” to meningitis. Transmission to other patients and family members, therefore, represents a significant health risk.


Bacteria capable of causing serious disease are present in the mouth and saliva of patients who may show no symptoms. Simple infection control precautions, such as use of gloves and a mask and effective hand hygiene practices, can prevent transmission to dental personnel, their families and their patients. This is particularly important for drug-resistant microorganisms. Prevention of transmission of tuberculosis requires prior recognition of infected or high-risk patients and prompt referral for diagnosis and treatment. Elective dental treatment for patients with active tuberculosis should be delayed until the patient is considered noninfectious. Patients with active tuberculosis who require emergency dental treatment should be referred to an appropriate facility.7

Dr. John is section head, infection control, London Health Sciences Centre and St. Joseph’s Health Care, London, Ontario.

Correspondence to: Dr. Michael John, Microbiology and Immunology, London Health Sciences Centre, Victoria Campus, Westminster Site, 800 Commissioners Road E., London ON N6A 4G5. E-mail: michael.john@lhsc.on.ca.  

The views expressed are those of the author and do not necessarily reflect the opinion or official policies of the Canadian Dental Association.


1. Mayhall, G, editor. Nosocomial infections in dental, oral and maxillofacial surgery in hospital epidemiology and infection control. 2nd ed. Baltimore: William & Wilkins; 1999.

2. Smith WH, Davies D, Mason KD, Onions JP. Intraoral and pulmonary tuberculosis following dental treatment. Lancet 1982; 1:842-4.

3. Cleveland JL, Kent J, Gooch BF, Valway SE, Marianos DW, Butler WR, Onorato IM. Multidrug-resistant Mycobacterium tuberculosis in an HIV dental clinic. Inf Control Hosp Epidemiol 1995; 16:7-11.

4. Shahin R, Johnson IL, Jamieson F, McGeer A, Tolkin J, Ford-Jones EL. Methicillin-resistant Staphylococcus aureus carriage in a child care center following a case of disease. Toronto Child Care Centre Study Group. Arch Pediatr Adolesc Med 1999; 153:864-8.

5. Goetz A, Posey K, Fleming J, Jacobs S, Boody L, Wagener MM, Muder RR. Methicillin-resistant Staphylococcus aureus in the community: a hospital-based study. Infect Control Hosp Epidemiol 1999; 20:689-91.

6. Rossi T, Laine J, Eerola E, Kotilainen P, Pettonen R. Denture carriage of methicillin-resistant Staphylococcus aureus. Lancet 1995; 345:1577.

7. Cleveland JL, Gooch BF, Bolyard EA, Simone PM, Mullan RJ, Marianos DW. TB infection control recommendations from the CDC, 1994: considerations for dentistry. United States Centres for Disease Control and Prevention. JAMA 1995; 126:593-9.