Anosmia (the loss of smell sense) has been closely correlated with COVID-19 infection.1–3 Multiple studies have described anosmia as an early2,4–9 and possibly sole10 symptom of COVID-19 infection. For employers, the inclusion of a self-report question asking about smell loss may be part of the entrance screening procedure, along with questions about the other COVID-19 symptoms.11 However, self-reporting of smell abnormalities underestimates the true prevalence of olfactory dysfunction.12,13 Zahra et al14 indicated that the presence of olfactory and taste dysfunction can potentially be used as a screening tool for COVID-19 especially in young and female patients. A multicenter European study reported that up to 85.6% of the patients with COVID-19 reported olfactory dysfunction, and among the 18.2% of patients in their study without nasal obstruction or rhinorrhea, 79.7% experienced anosmia.3
Globally, many regions do not have access to the community-level COVID-19 testing resources that are available in North America and the European Union. In these resource limited regions, it is imperative for employers to have efficient methods for increasing the accuracy of their current screening processes. To date, this largely includes a temperature check and self-reported symptom survey prior to entering the site.15 The use of a screening test to decipher olfactory dysfunction has not been widely used.
The primary intent of this paper is to describe an “active” entrance screening for olfactory dysfunction that is used in parallel with temperature assessment and symptom screening survey during the entrance screening protocol. The secondary purpose is to quantify the sensitivity and specificity of this additional screening procedure.
Site and Participant Selection:
Study locations were selected based on COVID-19 epidemiological activity (either high regional prevalence of COVID-19 or high number of employees failing the established screening protocol which included temperature assessment and symptom survey). The testing was performed on 4120 employees from April to July 2020 at multiple meat packing plants in Latin America, including Ecuador, Chile, and Brazil.
The Assessment of Olfactory Ability
An “active” screen for olfactory dysfunction using water and vinegar was conducted on all individuals entering the facility during the study period. The “screeners” were trained for: the olfactory test procedure, employee disposition based on results, and record keeping. The screeners used appropriate personal protective equipment (face shield, N95 mask, gloves, and gown) and were provided the testing supplies in Fig. 1.
The screener saturates one applicator in vinegar and a second applicator in water prior to an individual entering the preselected screening area. The screener gives employee instructions on how to properly perform the olfactory test. The applicators are handed to the employee to smell. If he/she perceives the odor, the test is considered negative. If an employee fails to identify the smell of the substance, the result is considered positive, the employee fails the entrance screening process.
The Assessment of RT-PCR
All 4120 employees were tested for COVID-19 infection with reverse transcription polymerase chain reaction method (RT-PCR).
RT-PCR was used as the “Gold Standard” for detecting the presence of COVID-19 infections. A positive test was defined by the presence of olfactory dysfunction in perceiving vinegar from water. The sensitivity, specificity, positive predicted value (PPV), negative predicted value (NPV), false positive rate, false negative rate, etc were calculated.
Table 1 presents the basic testing results of both olfactory dysfunction and RT-PCR and for 4120 subjects. Statistical analysis of the olfactory test data from Table 1 is presented in Table 2. RT-PCR tests were positive for 12.5% of subjects. With an overall accuracy at 79.8%, the sensitivity and specificity of the active olfactory screening examination was 41.2% and 85.3%, respectively. Negative predicted value (NPV) was 91.0%, which was the false negative rate among all test negatives. Out of the 4120 individuals who were screened, 55 out of 517 (10.6%) of those who tested positive for COVID-19 had a change in olfactory function as their only symptom. Over 25% (55 out of 213 [25.82%]) had an alteration in olfaction as the only symptom among PCR positive cases.
TABLE 1 -
The Basic Testing Results
||RT-PCR Test Result
|Smell loss on active screening (vinegar/water test)
| With other symptoms
| Without other symptoms
RT-PCR, reverse transcription polymerase chain reaction.
TABLE 2 -
Indicators for Evaluation of Smell Loss Testing as a Screening Tool
|Prevalence = (A + C)/All
||Prevalence of COVID 19 infection in the population tested
|Sensitivity = A/(A + C)
||True positive % among cases
|Specificity = D/(B + D)
||True negative % among no cases
|Positive predicted value PPV = A/(A + B)
||True positive % among all test positives
|Negative predicted value NPV = D/(C + D)
||True negative rate % among all test negatives
|False positive rate = B/(A + B)
||False positive % among all test positives
|False negative rate = C/(C + D)
||False negative rate % among all test negatives
|Rate ratio for testing out the disease = A/(A + B)/C/(C + D)
||Likelihood to be diagnosed if positive
|Positive likelihood ratio (LR+) = Sensitivity/(1–specificity)
||True positive rate/false positive rate
|Negative likelihood ratio (LR–) = (1–sensitivity)/specificity
||False negative rate/true negative rate
|Accuracy = (A + D)/All
||Overall probability that a patient is correctly classified
The early detection and separation of individuals with COVID-19 from entering the workplace is crucial to containing the spread of this disease in the workplace. Previous reports discussed anosmia as an important early indicator of COVID-19 infection.2,4–9 Yet self-reporting of smelling abnormalities has proven to be an insensitive indicator of true changes in olfaction and can underestimate its true prevalence in a screened population.12,13 Active screening for anosmia therefore, could be a valuable additional tool in detecting occult SARS-CoV-2 infections, thus improving the ability for employers to prevent further spread of this disease in the workplace.
Current screening methods in most workplaces include temperature screening and self-report symptom surveys.11 The scientific community has questioned the benefit of temperature screening as a high-cost and low-yield tool for COVID-19 screening16 and described it as “notoriously inaccurate.”17 The detection of a COVID-19 positive case by temperature screening and symptom surveys has an observed yield of approximately one identified case per 85,000 screened.18 Despite this information, many employers continue to allocate resources for temperature checking and symptom screening and have not, to date, incorporated other screening tests that will improve the detection rate.
In our study, vinegar was selected as an additional test modality. The US Army's in South Korea found that use of vinegar was an effective way to assess smell dysfunction.19 We found the sensitivity of the active vinegar smell screening examination was low, 41.2% (false positive at 71.3%). Therefore, the vinegar test may not be a good candidate as the first screening test in a sequential algorithm but would be valuable in a parallel algorithm that combines temperature screening and symptom survey. The rate ratio for testing the disease was 2.90, which can still increase the likelihood of identifying the infection by itself.
The specificity of olfactory test was 85.3% and negative predictive value was 91.0%, which indicate that this test could be a very good screening tool to confirm the absence of disease. Interestingly, our results demonstrate that 55 out of 517 (10.64%) of employees who tested positive for COVID-19 had loss of smell as their only symptom. These individuals would not have been identified with standard screening measures.
One limitation in this study was that our dataset did not include temperature or self-reported symptom data. Although temperature screening was performed on each employee, and any employee with a temperature more than 38 °C was asked to follow up with a healthcare provider, we did not include these in our analysis because our intent was to determine the utility of an active screening test for olfactory function.
In conclusion, initial screening tests should have high sensitivity. Although the sensitivity of the olfactory test is relatively low, it could be used to augment the sensitivity of current screening tests in a parallel algorithm. The active olfactory test demonstrates high specificity and can be useful to confirm the absence of disease in a worker population. In order to increase the overall sensitivity and specificity of an entrance screening process, parallel active testing for anosmia should be incorporated into the entrance screening protocol.
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