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Test criteria for coronavirus

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Anyone who has symptoms of COVID-19 should get tested

Anyone who has symptoms of COVID-19 should get tested


The following should be tested (further information about each point can be found in the collapsible box below): 

  1. Everyone with acute respiratory tract infection or other symptoms of COVID-19
  2. Everyone who has been exposed to infection to COVID-19, either as a close contact or after travel to countries or regions with high incidence during the last 10 days*
  3. Other groups can be tested after assessment by a doctor. If a person without symptoms and who has not been exposed is tested, a positive test must be confirmed with a new test.
  4. Anyone who suspects that they have COVID-19 should have the opportunity to be tested

*Children play a smaller role in transmission of COVID-19 than adults, so testing of children of primary school or child care age without symptoms will therefore be of less significance. However, testing can be carried out if desired and in consultation with parents/guardians.   

The doctor at the test centre is responsible for informing the patient and their regular doctor of the test result (both positive and negative test results), and for notifying the Norwegian Surveillance System for Communicable Diseases (MSIS) of any positive results on the same day they are available. Electronic MSIS notifications can be sent by a doctor, or by a nurse on behalf of a doctor.

Supplementary information about who should be tested

1) Test of everyone with symptoms of COVID-19

The Norwegian Institute of Public Health recommends that everyone with symptoms of COVID-19 should be tested as soon as possible.

This includes anyone with a newly arisen respiratory tract infection or other symptoms of COVID-19. COVID-19 often has the following symptoms; fever, cough, shortness of breath, loss of taste or smell, sore throat, or feeling unwell.

For residents of nursing homes, there should be an extremely low threshold for suspicion of COVID-19.

Children under the age of 10 with only mild symptoms of respiratory tract infection can be observed at home for a few days before testing. Children with a runny nose as the only symptom, who are otherwise in general good health without other signs of a newly arisen respiratory tract infection, do not need to be kept at home or tested.

Everyone who is tested should stay at home until a negative test result is available. With a negative test, they can return to work/school when their general condition is good (they feel well and have no fever), even though they still have some symptoms of respiratory tract infection.

For deaths in healthcare institutions where a doctor suspects that the patient had COVID-19, post mortem tests for COVID-19 should be performed.

2) Test of asymptomatic patients who have been exposed to COVID-19 infection

Anyone with a known exposure to COVID-19 infection within the last 10 days (close contacts, arrivals from high-incidence countries or other known exposure to confirmed cases) should be tested, even if they present no symptoms.

This includes the following groups:

  • Close contacts who have been quarantined. They can be tested to speed up further contact tracing, but the test result will not affect quarantine time. Suggested test date to detect most cases; day 5-7.
  • People who may be exempt from quarantine with negative test results. They should be tested as soon as possible, preferably on day 3 after the last exposure, and then at least 48 hours after the first test, preferably on day 7. They are then in quarantine until the first result is available and are in quarantine in their free time until the second result is available.
  • If infection is detected in a nursing home, all employees and residents of the affected units should be tested. 
  • People arriving in Norway from areas or countries with a higher incidence of COVID-19. Countries with a higher incidence are, for example, "red" countries. These can be tested to speed up further contact tracing, but the test result will not affect time in quarantine.

There is usually no basis for forcing people without symptoms to be tested, according to the Infection Control Act.

3) Test of others after assessment by a doctor

In some situations, people should be tested even if they have neither symptoms of COVID-19 nor have a known exposure to the disease.

This includes the following groups:

  • Employees in the healthcare system who work close to patients, including new employees and temporary staff who have been travelling outside Norway during the last 10 days, should be tested and not work close to patients until a negative test result is available.
  • Before new residents move into a nursing home, testing may be appropriate and is recommended if the nursing home resident has been travelling outside Norway.
  • Prior to certain hospital stays or procedures, testing may be appropriate. The hospitals themselves establish routines for this.
  • The municipal medical officer may, in some cases, consider that there is an indication for testing before moving into / starting in particularly dense living environments or workplaces with a high risk of infection, e.g. arrival centres, military camps, slaughterhouses and prisons.
  • Participants in research projects.

Positive test results among asymptomatic, non-infected individuals should be confirmed by a new test to improve the positive predictive value, see below.

4) Others who want to be tested

Other people who want to be tested but who do not have symptoms and do not suspect that they are infected can also be tested if there is available capacity. The test will then usually not be covered by the public sector. This may, for example, apply for health certificates.

Positive test results among asymptomatic, non-infected individuals should be confirmed by a new test to improve the positive predictive value, see below.

Recommended order of priority with a lack of testing capacity

If there is a lack of testing capacity, groups should be tested in the following order of priority: 

A) People with symptoms

  1. Patient in need of hospital admission
  2. Patient / resident in a nursing home or other healthcare institution
  3. Employee in the healthcare service with work that puts them in the vicinity of patients
  4. Person in a risk group, see risk groups and their relatives
  5. People who have been exposed to infection
  6. Other people with symptoms

B) People without symptoms who have been exposed to infection: 

  1. Outbreak situations in healthcare institutions
  2. A close contact to a confirmed case of COVID-19
  3. Healthcare personnel with patient contact who has been abroad
  4. Person who has been in quarantine after travel
  5. On arrival from abroad 

C) Others

2020-09-17 Flytskjema_engelsk.png

Waiting for test results

The main rule is that anyone who has been tested must stay at home until their test result becomes available. Household members do not have to be in quarantine, nor do household members who work in the healthcare service.

There are two exceptions to the main rule:

  • People who have been tested even though they have no symptoms or have not been exposed to infection, do not have to stay at home awaiting a test result.
  • Close contact(s) who have been highly exposed to infection (household member or equivalent close contact), have symptoms compatible with COVID-19 AND who cannot be tested / will take a long time before the test result is available, can be treated as "probable COVID-19" pending test results. This means that the patient is in isolation and household members and equivalent close contacts are in quarantine until test results become available.

Interpreting the test results

The PCR-test for COVID-19 is a good test with very high specificity and good sensitivity. It is estimated that the clinical specificity is around 99.999 per cent and that the clinical sensitivity is around 80 per cent. The sensitivity of the test depends on which stage of the disease the infected person is and is highest in the days around the onset of symptoms. Then it is probably over 90%. In the majority of cases, the test results are reliable. However, no test is completely accurate and the result must be interpreted according to the probability that the person is infected.

If the test result is negative, and there is still a strong clinical suspicion of COVID-19, a new test should be taken.

If the test result is positive, the person is not a close contact, the infection burden in society is low and the person is asymptomatic, a new test should be taken and be analysed as quickly as possible to confirm the result.

In the event of a known infection in recent months, a positive PCR test result must be interpreted with caution. This is because non-infectious virus residues (non-replicable RNA) can be detected by PCR for a long time (up to two to three months) after the person is no longer contagious. This should also be considered in case of a weakly positive result in an asymptomatic person without an increased risk of infection, as most of those with a weakly positive PCR (Ct value above 33) will be past the contagious period.

2020-08-28 Flytskjema testresultat_engelsk.png

Positive test result from people without symptoms

A person without symptoms who has NOT been exposed, has a very low probability of being infected. A positive test result should be confirmed with a new test as soon as possible. A new positive test result will increase the positive predictive value significantly. While waiting for the confirmatory test result, act as if the result is positive. 

  • With a new positive result (and the person still has no symptoms), it can be assumed to be a true positive result. There are estimated to be fewer than 1 false positive result per 100 true positive results.
  • With a negative result from the confirmatory test, because of the low probability of a positive result, it is overwhelmingly likely that the negative result is correct. The conclusion is therefore that the result is negative and further testing is not necessary as long as the person continues to have no symptoms. 

With a positive test result for a person without symptoms who has been exposed to infection during the last 10 days, it is most likely that the answer is true positive. 

Negative test results from people with symptoms 

The probability of a false negative test should be considered based on whether the person is a known close contact, clinical suspicion, time since symptom onset and other test results such as CT-thorax.

  • If there is clinical suspicion of COVID-19 and a negative test response, the person should be retested. With a pre-test probability of infection of 30 per cent, a new test will reduce the probability of false negative test results from 8 per cent to 1.7 per cent (at 80 per cent sensitivity of PCR test).
  • Tests from other localisations such as BAL, saliva, should be considered.

COVID-19-related test results at helsenorge.no and in Summary care records

COVID-19-related test results from the newly established NIPH laboratory database will appear on Helsenorge.no as soon as the samples are analysed and reported. The test results are sent from all the country's laboratories to the laboratory database in the Norwegian Surveillance System for Communicable Diseases (MSIS) at the Norwegian Institute of Public Health, at the same time as they are sent to the doctor.

The patient must log on to Helsenorge.no with electronic ID. Information has been prepared that can be distributed to the patient during testing.

COVID-19 related test results appear in the summary care record as soon as they are analysed and released by the laboratory. Specimens that are not analysed in medical microbiological laboratories (for example, COVID-19 rapid tests) are not shown here. The following infectious agents are defined by the Ministry of Health and Care Services as COVID-19 related infectious agents. The list is updated as of 2nd July 2020, and will be continuously updated at helsenorge.no:

  • SARS-CoV-2
  • SARS-CoV-2 antibodies
  • Influenza A / Influenza B
  • Parainfluenza virus
  • RS virus (Respiratory syncytial virus)
  • Human metapneumovirus
  • Adenovirus
  • Rhinovirus
  • Mycoplasma pneumonia
  • Chlamydia pneumonia
  • Bordetella pertussis (whooping cough)

About the solution:

Why is testing of people without symptoms and without exposure not usually recommended?

Even with unlimited access to tests, it will usually not be advisable to test people without symptoms and have not been exposed to infection.

This is because:

  • A negative test can give a false sense of security. The test result only gives a snapshot of the situation. A person with a negative test result may be in the incubation phase and not yet be sick.  
  • A positive PCR result may show infection that has passed and is no longer contagious. The PCR test detects the virus's genetic material and does not distinguish between viral fragments and an infectious virus. Viral fragments may be present in the respiratory tract for weeks after the infection has passed.
  • Increased probability of false positive results where there is low transmission in society (low positive predictive value). 
    With a prevalence of 0.005 per cent (probable prevalence among people without symptoms in Norway today), the positive predictive value would be around 80 per cent. That is, 2 out of 10 who test positive are not infected with SARS-CoV-2. If a new test is taken, the positive predictive value will improve to over 99.99 per cent.
  • With low prevalence, on average, many tests need to be taken to find a true positive, see table below.
Table: Significance of prevalence for how many need to be tested and expected results. Given clinical sensitivity of 80 per cent, specificity of 99.999 per cent.

Prevalence in the population to be tested

30 %

3 %

1 %

0.005 % (as in Norway today)

0.001 %

Number who need to be tested to find a true positive

4

42

125

25 000

125 000

Probability for a true positive result (positive predictive value)

99.99 %

99.88 %

99.65 %

80 %

44.4 %

Number of false positive results expected per true positive

0.00003

0.0004

0.0012

0.25

1.25

Figures 1 and 2 below show examples of testing of 100 000 individuals (without symptoms, not exposed, randomly selected) with a prevalence of 0.01 per cent and 3 per cent, respectively, and with clinical sensitivity of 80 per cent and specificity of 99.999 per cent.

Fig 1 PPV NPV English15.09.2020.JPG
Figure 1.
Figure 2.

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Facts

Coronavirus

SARS-CoV-2 is the name of the virus that is causing the outbreak of COVID-19 disease.

The virus is related to another coronavirus that caused the SARS outbreak in 2002/2003 but is not the same virus.