After a careful reading of the interesting comments by Lippi et al.1 on the work “Utility of preoperative polymerase chain reaction testing during SARS-CoV-2 pandemic: The challenge of evolving incidence”,2 the undersigned authors believe it is appropriate to make some clarifications. In the article, the authors did not question the value of screening asymptomatic carriers using reverse transcription–polymerase chain reaction (RT–PCR), a test that has demonstrated high efficacy in terms of sensitivity and specificity, but rather its performance depending on each epidemiological scenario. In the conclusions, the authors questioned “the usefulness of preoperative RT–PCR to detect asymptomatic carriers […] in very low prevalence scenarios […]”, and they did so assuming RT–PCR performances (based on the sensitivity of the test) higher than those proposed by Lippi et al.1 and other authors.3–5 As the authors explained in the discussion, the diagnostic performance of a test worsens as its sensitivity decreases: “for a constant cumulative incidence, the number of tests necessary to detect a positive increases as the sensitivity of said test decreases.” Likewise, the lower the sensitivity, the greater the probability that a carrier will not be detected with the test (false negative). If we assume a sensitivity of RT–PCR to diagnose SARS-CoV-2 infection that could range between 85% and 50% depending on the circumstances, as proposed by Lippi et al.,1 the diagnostic performance of the test worsens and greater uncertainty is generated in the face of a negative result.
The authors agree with Lippi et al. in their assessments of the severity of the pandemic and its impact on the surgical field, but consider that they have misinterpreted their conclusions when they state that “we disagree with the conclusion that the rate of asymptomatic surgical patients is always insignificant in low prevalence scenarios”, a statement that the authors never made. When the article was written, in the first months of the pandemic, none of the 2722 tests performed (4520 at the time of manuscript submission) had been positive, so the authors inferred that the rate of asymptomatic carriers was lower than that estimated based on data published by different government offices (simulation 2).2 With these data it was not possible to discern whether the rate of asymptomatic carriers was close to that estimated in simulation 1. In this case, 38,461 tests would have been necessary to detect a true positive.
In order to compare the performance of the test depending on the epidemiological moment, the authors defined “performance” as the number of tests necessary to perform for the detection of a true case (a variable, therefore, dependent on sensitivity and prevalence). What was intended to be highlighted with this approach was that in pandemic situations with evolution in waves, such as that caused by SARS-CoV-2, in conditions of incidence falling to very low levels, the effectiveness of the diagnostic test or its performance, measured in the terms that were proposed, is logically reduced in a significant way, and that this factor is transcendental when defining action policies. In fact, the consensus protocols currently in force in Spain and published in May 20214 propose a non-indiscriminate use of preoperative RT-PCR based on the joint analysis of four variables: a) prevalence of infection; b) immunological status of the patient; c) patient comorbidity, and d) degree of invasiveness of the surgery, with the epidemiological situation, defined by the estimated prevalence, being the key element in decision-making: “If the epidemiology of the area is favourable, at alert level 1, there is no high risk for the patient, nor high risk for surgery, PCR could be omitted and only clinical-epidemiological screening performed 10 days and 72 hours before the intervention. If, in addition, the risk of surgery is low, screening could also be omitted in the 10 days prior to the intervention”.4
Taking into account the above considerations, the authors agree with Lippi et al. when they state that “widespread screening for SARS-CoV-2 in asymptomatic populations is unnecessary, and perhaps unjustified for various social, economic, and diagnostic reasons,” and that “Efficient testing protocols are essential in reducing risks, in-hospital outbreaks and protecting the most vulnerable patients (i.e., the immunocompromised and the elderly).” Indeed, the authors believe that this statement is compatible with their original approach and that both are supported by the aforementioned recommendations. The authors are convinced that making quick decisions in extreme situations sometimes involves applying measures that must then be reconsidered or “fine-tuned.” Time and data allow these measures to be refined based on rational and reasonable criteria, and this form of action is what scientific societies and regulatory bodies have followed in the case of the SARS-CoV-2 pandemic.
FundingNone.
Author contributionsDe la Matta M, Delgado-Sánchez JM and Martín-Gutiérrez G are the sole authors of the response text to the letter to the editor of Lippi et al. “Negative preoperative RT-PCR screening is no guarantee of no SARS-CoV-2 infection”.
Conflict of interestsNone.
