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.