Modelling the risk for patient-to-patient transmission of blood-borne viruses associated with the absence of sterilization of dental handpieces

Background: A few national or local surveys revealed in 2008 a poor adherence of French dentists to national recommendations for sterilization of handpieces (DH) between each patient. The French Health Ministry therefore asked the national public health surveillance institute (InVS) to assess the risk in such a case for patient-to-patient transmission of blood borne viruses (BBV) - human immunodeficiency virus [HIV], hepatitis B |HBV] or C [HCV] - in order to decide whether or not a systematic information and screening of exposed patients was necessary

Objective: To provide a quantitative assessment of the risk for patient-to-patient transmission of HIV, HBV and HCV when handpieces in dental surgery are not sterilized.

Methods: A modelling approach was adopted for this assessment. The probability of transmission of HIV, HBV and HCV during a dental care without sterilization of DH between patients was calculated taking into account the probability of viral contamination of DH during a dental care, the likelihood of transmission during a dental care with a reused, non-sterilized contaminated DH, and the proportion of patients susceptible to each BBV. We used multiplicative models based upon parameters from the literature or determined by experts. Several scenarios took into account various probabilities of persistence of DH viral contamination

Results: For an intermediate scenario of gradual decrease of the viral contamination of the DH, the likehood of contracting a BBV infection when DH were not sterilized was the lowest for HIV (1 for 420 millions dental care sessions) and the highest for HBV (1 for 516,000 sessions). The probability of occurrence of at least one BBV transmission in a cohort of 1,000 patients followed for one year in a dental care setting ranged from 1/90 000 for HIV to 1/120 for HBV. These results should be interpreted with caution as the models did not take into account the effect of disinfection of DH, a practice often reported by dentists, which efficacy however is not known. In addition, the models were based upon parameters with uncertainty, which justify further sensitivity analysis.

Conclusions: This assessment was helpful for decision-making as the literature was poor on the topic. The low level of risk did not advocate for a systematic information of patients exposed to dental care in a setting not complying with current recommendations for sterilization of DH. This decision should be taken on a case by case basis, taking into account this assessment and findings from the investigation, particularly about other infection control practices. However, even if the risk we assessed was low, it justifies a strict observance of standard precautions and recommendations for good sterilization practices in dentistry.