Current best evidence for clinical care (more info)
INTRODUCTION: Despite the limited evidence for its effectiveness, thermal screening at points of entry has increasingly become a standard protocol in numerous parts of the globe in response to the COVID-19 pandemic. We sought to determine the effectiveness of thermal screening as a key step in diagnosing COVID-19 in a resource-limited setting.
MATERIALS AND METHODS: This was a retrospective cross-sectional study based on a review of body temperature and Xpert Xpress SARS CoV-2 test results records for truck drivers entering Uganda through Mutukula between 15th May and 30th July 2020. All records missing information for body temperature, age, gender, and Xpert Xpress SARS CoV-2 status were excluded from the data set. A data set of 7,181 entries was used to compare thermal screening and Xpert Xpress SARS CoV-2 assay test results using the diagnostic statistical test in STATAv15 software. The prevalence of COVID-19 amongst the truck drivers based on Xpert Xpress SARS CoV-2 assay results was determined. The sensitivity, specificity, positive predictive value, negative predictive value, positive and negative Likelihood ratios were obtained using Xpert Xpress SARS CoV-2 assay as the gold standard.
RESULTS: Based on our gold standard test, the proportion of persons that tested positive for COVID-19 was 6.7% (95% CI: 6.1-7.3). Of the 7,181 persons that were thermally screened, 6,844 (95.3%) were male. The sample median age was 38 years (interquartile range, IQR: 31-45 years). The median body temperature was 36.5°C (IQR: 36.3-36.7) and only n (1.2%) had a body temperature above 37.5°C. The sensitivity and specificity of thermal screening were 9.9% (95% CI: 7.4-13.0) and 99.5% (95% CI: 99.3-99.6) respectively. The positive and negative predictive values were 57.8 (95% CI: 46.5-68.6) and 93.9 (95% CI: 93.3-94.4) respectively. The positive and negative Likelihood Ratios (LRs) were 19 (95% CI: 12.4-29.1) and 0.9 (95% CI: 0.88-0.93) respectively.
CONCLUSION: In this study population, the use of Thermal screening alone is ineffective in the detection of potential COVID-19 cases at point of entry. We recommend a combination of screening tests or additional testing using highly sensitive molecular diagnostics such as Polymerase Chain Reaction.
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This paper offers evidence to confirm that thermal screening offers little other than 'security theater' when trying to screen and prevent COVID-19 cases. This study is unlikely to be the last word in the matter, but provides more evidence for what will ultimately likely emerge as the consensus.
The study showed that this screening by itself is useless. That is an important message for health authorities to avoid wasting effort and time.
The utility (or lack thereof) of thermal screening is likely not new information. The predictive values of the tests used may be relevant if the reader is interested in those specific tests. The threshold for defining fever was quite low for discriminating illness, however, the prevalence was sufficiently low that that this is not a concern in this study. The importance of a one-time screening with either test wasn't discussed in detail to determine whether measurements (as are done at air crossings in some countries) would be feasible.
Thermal screening for the detection of COVID-19 is known to have very low sensitivity but high specificity, so the results of this study are not surprising. The cost of the procedure is low and the high (but not extremely high) specificity, in my view, makes it a desirable procedure when you want to check a large number of persons before entrance in a structure where Covid-19 cases could spread the infection.