[Utility of preoperative polymerase chain reaction testing during SARS-CoV-2 pandemic: The challenge of evolving incidence].

Introduction: Due to its high transmissibility, measures aimed at reducing the spread of SARS CoV2 have become mandatory. Different organizations have recommended performing polymerase chain reaction tests (PCR) as part of the preoperative screening of surgical patients. We aimed to determine the performance of PCR testing to detect asymptomatic carriers.
Methods: Observational study carried out at a tertiary care center. We compared the results of preoperative real-time reverse-transcription-PCR test (RT-PCR) performed on a cohort of patients pending surgery with the results we would have expected assuming the epidemiological data released by government offices.
Results: We registered no positives in the 2,722 preoperative RT-PCR tests performed in our health care area between epidemiological Weeks 18 to 21, meaning a cumulative incidence trending to zero. Assuming public epidemiological data, the probabilistic projection of potential asymptomatic individuals ranged from 0.27*10e -4 (according to official data of new cases diagnosed by PCR) to 4.69*10e -4 if we assumed cases confirmed by IgG test in our province. Assuming a RT-PCR sensitivity of 95%, to obtain a positive result we should perform 38,461 and 2,028 tests respectively. Conclusions: In scenarios of very low prevalence and despite high sensitivity scores, indiscriminate preoperative RT-PCR screening is of a questionable effectiveness for detecting asymptomatic carriers. Our findings evidence the difficulty of establishing reliable predictive models for the episodic and rapidly evolving incidence of infections such as has characterized the SARS CoV2 pandemic.