Infection Control: Update on Immunization

by Gillian M. McCarthy, BDS, MSc.

Knowledge of infectious diseases and recommendations for infection control are in a constant state of flux as familiar microorganisms evolve and others emerge to produce new challenges. Our efforts to keep pace with these changes and to protect our patients, staff and ourselves can be frustrating, because we only have a partial understanding of pathogens at any point in time, and information rapidly becomes outdated. There is a growing respect for the ability of viruses and bacteria to outwit the human host and an increasing concern that our vulnerability to infectious diseases exceeds our capacity to produce effective antimicrobial drugs.

Despite this, we can take some comfort from the success of immunization programmes in controlling many infectious diseases in the 20th century, and the recognition that immunization has been particularly effective in reducing the risks of infection for healthcare workers. It is recommended that dental workers in Canada should be adequately immunized against measles, mumps, rubella, influenza, tetanus, diphtheria, hepatitis B virus and varicella. BCG immunization is not recommended in North America unless an individual is at high risk of tuberculosis. Because of the importance of prevention of transmission of HBV and the recent licensing of a varicella vaccine in Canada these will be discussed in greater detail.

Recommendations have been recently published to promote the use of varicella vaccine to control varicella and herpes zoster. It is hoped that all provinces or territories will have routine childhood varicella vaccination programmes by 2005, and that all healthcare workers and trainees will be immune to varicella by 2003. Dentists and staff need an assessment of their susceptibility (a reliable history of varicella is satisfactory – otherwise serology should be performed) and those who are not immune should receive immunization. This is particularly important for dental workers who care for young children or immunocompromised patients.

The introduction of a vaccine to protect against hepatitis B virus has dramatically reduced occupationally acquired infections in healthcare workers and the potential for transmission of HBV from healthcare workers to patients. An HBV immunization program for school children has recently been introduced in Canada, in addition to screening for pregnant women. These initiatives should have a major impact on the prevalence of HBV in the general population in future decades. However, HBV will continue to be a major hazard for susceptible dental workers in the foreseeable future. Ninety-four percent of dentists in Canada report HBV immunization or naturally acquired immunity. It is tempting to believe that 94% of dentists may be immune to HBV, however this is very unlikely. Although 95% of children and young adults develop an adequate response, the efficacy of HBV vaccine decreases with age, smoking, obesity and chronic disease. Recipients of HBV vaccine with an anti-HBs titre of more than 10 mIU/ml are considered to have virtually complete protection. Up to 50% of non-responders will respond after additional doses of vaccine. The proportion of HBV vaccine responders would be maximized if all recipients had appropriate post-immunization serology and any non-responders were given additional doses. Unfortunately, nearly one third of dentists in Canada reported no antibody testing after HBV immunization, and therefore lost the opportunity to check their response or to receive additional dose(s) of vaccine if necessary. This raises the possibility that many dentists may have a false sense of security, and be susceptible to HBV despite immunization.

Gillian M. McCarthy, BDS, MSc., is a Career Scientist of the Ontario Ministry of Health, Health Research Personnel Development Program and has been recently appointed Professor in the Faculty of Medicine & Dentistry at The University of Western Ontario in the School of Dentistry and the Department of Epidemiology and Biostatistics. Dr. McCarthy is a contributing consultant to Oral Health, infection control and health issues.