The demand for rapid COVID-19 testing
Massive and regular testing for coronavirus infection is an essential limiting factor in the spread of the pandemic. If you detect an infection early, you can take protective measures and protect others from disease. The urgent need to identify infected people persists even one year after the outbreak of the pandemic.
Existing molecular tests for COVID-19 do not allow for regular screening of the entire population for infection. The main disadvantages of existing PCR tests:
- few tests are carried out: no more than 10% of the total number of people;
- tests are expensive to test the entire population;
- the time from taking a sample to getting a result can be calculated in hours and days;
- testing cannot be carried out without expensive equipment and highly qualified specialists.
An alternative strategy for testing for coronavirus infection is to monitor olfactory dysfunction — anosmia. A standardized test for olfactory defects does not require special skills or equipment. It quickly shows the result, can be performed independently, and is ten times cheaper than a PCR test.
Olfactory dysfunction in COVID-19
Anosmia is a feature of coronavirus disease that distinguishes it from other respiratory infections, such as influenza. Olfactory defects are 4 to 10 times more likely to be associated with COVID-19 than fever.
This symptom is detected in 41-53% of cases with independent observation. Moreover, when using a standardized olfactory test, COVID-19 is seen in 76-83% of cases, including asymptomatic ones. In some instances, anosmia precedes other symptoms of the disease: shortness of breath, cough, diarrhea.
The relevance of modeling the effectiveness of olfactory tests
American scientists from the universities of Harvard, Yale, and Colorado have modeled an olfactory test’s effectiveness to limit the spread of the COVID-19 pandemic. Their work is a continuation of a series of modeling studies that show that the frequency of testing and the speed of obtaining a result are crucial for limiting the pandemic, and the sensitivity of the test is secondary.
In the simulation, the scientists assumed that olfactory dysfunction testing:
- was cheap enough to be performed frequently;
- you can do it yourself and get the result in a few minutes.
General modeling parameters
Scientists presented the entire population in the form of four groups: susceptible to infection, prone to disease, infected, and ill.
The size of the simulated group was 20,000 people. For comparison: so many people study at a large university.
The level of external infection for the simulated group was constant with infection penetration rate into one case per day. The level of susceptibility to the disease and the duration of illness were taken from an authoritative source.
Scientists have put in the model the rule that people with detected olfactory dysfunction will go to self-isolation.
The model also considers that 35% of patients will secrete a viable virus over a long time. This assumption made it possible to model the viral dynamics more accurately.
Simulations suggested that 80% of the population participates in olfactory function monitoring, with 4% of people having olfactory dysfunction independent of COVID-19.
Monitoring of smell deters the spread of COVID-19
Daily detection of olfactory defects prevented outbreaks of the disease, provided that the symptom was present in 50% of cases of the disease.
If the prevalence of anosmia was 75% of the time, then olfactory testing performed every 3 days was more effective than weekly PCR testing with a one-day lead time (schedule A).
After the scientists estimated the average number of people infected by one infected person, they could predict the testing strategy’s effectiveness depending on the transmission scenario (graph B).
The earlier anosmia is detected – the less likely the COVID-19 outbreak is
Olfactory dysfunction is an early symptom of COVID-19. However, there is still little data on the timing of anosmia’s appearance in different people in the scientific literature. The researchers modeled the effect of olfactory dysfunction testing on the timing of symptom detection.
Model parameters:
- anosmia was present in 75% of infected patients;
- the duration of anosmia was 7 days.
It was found that if the olfactory defects appeared within 2 days of the onset of the disease, then testing daily or every three days was enough to prevent the spread of the infection from developing into an outbreak (a sharp increase in the number of diseases).
For the case where anosmia appeared within 3 days of the disease’s onset, the increase in the epidemic was already poorly controlled by testing every 3 days. However, daily olfactory monitoring remained a useful tool to contain the outbreak.
Weekly testing was ineffective.
How many times a week to conduct an olfactory test for COVID-19?
Additional simulation demonstrates the effectiveness of testing olfactory dysfunction even with a decrease in anosmia duration.
Model parameters:
- anosmia was present in 75% of infected patients;
- loss of sense of smell occurred one day after infection;
- duration of the symptom: 1, 3, 5, or 7 days.
It was found that checking olfactory dysfunction once every 3 days is sufficient if the symptom’s duration is from 3 to 7 days.
An unlikely scenario of anosmia duration is only one day. However, daily testing was effective even in this situation. Daily testing was also influential in a problematic case where olfactory dysfunction appeared 3 days after the disease’s onset and lasted only one day.
Weekly testing of the sense of smell was not enough to prevent an explosive increase in the incidence:
Olfactory dysfunction testing mitigates disease outbreak
Scientists have evaluated the effectiveness of olfactory testing during an outbreak that has already begun. In this model, testing started only if 2% of the population was already infected.
Model parameters:
- anosmia was present in 75% of infected patients;
- olfactory dysfunction appeared a day after the onset of the disease;
- the duration of the symptom is 7 days.
It was found that testing daily or every three days was sufficient to contain the increase in morbidity:
Conclusions
The scientists demonstrate that monitoring olfactory dysfunction can help manage the COVID-19 pandemic with their work.
Calculations show that weekly PCR testing reduces the average number of people infected by one infected person by 42%. Testing the sense of smell reduces the same indicator by 55%. Moreover, the test itself is cheaper in the second case, but there are no personnel and protective equipment, collection, and sample transportation costs.
The frequency of testing and the speed of obtaining results play a leading role in controlling the epidemic’s spread.
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Modeling the effectiveness of olfactory testing to limit SARS-2-CoV transmission
