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Test criteria for coronavirus

Published Updated

Anyone who has symptoms of COVID-19 should be tested.

Anyone who has symptoms of COVID-19 should be tested.


The following should be tested: 

  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.* It is particularly important that new arrivals from Denmark are tested. 
  3. Other groups can be tested after assessment by a doctor. 
  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.   

When people without symptoms and who are not exposed to infection are tested, positive test results should be confirmed by a new test. 

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 a few symptoms after the 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 of lower secondary school age and above 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; between day 3 and 7, preferably day 5.
  • Some cross-border workers may be exempt from quarantine during working hours during testing, see the exemption provisions and test regime in §6b and 6c of the COVID-19 regulations. For personnel in critical functions in society who are covered by the exemption from the entry and infection quarantine mentioned in §6e, it is also strongly recommended, if possible, to carry out a test regime as described in §6c. The exemption can only be used in cases where it is necessary to avoid danger to life and health.
  • 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 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.
  • 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 cost of 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

2020-11-02 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.
  • People who are in quarantine who have symptoms compatible with COVID-19 are considered as "probable COVID-19" pending test results. This means that the person who is sick 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 test result. There are estimated to be fewer than 1 false positive analysis result per 1000 true positive analysis 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 analysis result 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

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.

Many viruses and bacteria can cause respiratory tract infections. In the search for the correct diagnosis, it may be necessary to request other tests in addition to SARS-CoV-2. Analysis results from the COVID-19 tests and other additional tests will be available to the patient on the test results website at helsenorge.no. The person ordering the tests should explain to the patient what they are being tested for.

COVID-19 related test results appear in the summary care record (for healthcare personnel) and the website for the test results on helsenorge.no (for patients) 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 analysis 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 (false positive analysis result). 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. For evaluation of prevalence in Norway, read the weekly reports. It is noted that the prevalence will be higher in a population with symptoms or has known infection exposure compared to a population without symptoms or increased risk of transmission.

Prevalence in the population to be tested

30 %

3 %

1 %

0.005 % 

0.001 %

Number who need to be tested to find one true positive case

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 analysis results expected per true positive analysis result

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 0.005 per cent and 3 per cent, respectively, and with clinical sensitivity of 80 per cent and specificity of 99.999 per cent.

Figur ppv og NPV
2020.11.23 figur PPV og NPV engelsk  fig 2.jpg

Figure 1 and 2: The figures show that with low prevalence/ probability, false positive results are the biggest problem, whereas with high prevalence/ probability, false negative results are the biggest problem.

Flowcharts

History

23.11.2020: Added some clarifications, to make it clear that these are analysis results. Updated Figures 1 and 2.

19.11.2020: minor change to paragraphs about test results.

18.11.2020: edited section about COVID-19- related test results. Added link to test results page on helsenorge.no

10.11.2020 Added that it is particularly important that new arrivals from Denmark are tested because of findings of mutated virus.

04.11.2020: Updated flowchart under C) Others.

02.11.2020: Added that it is recommended that all close contacts of lower secondary school age and above are tested.

23.09.2020: Small changes in the numbers in figures 1 and 2 that show examples of testing of 100 000 individuals (without symptoms, not exposed, randomly selected).

22.09.2020: Clarified "even though they still have a few symptoms after the respiratory tract infection." Added "Since both viruses and bacteria can cause respiratory tract infections or other COVID-19 related symptoms, other tests in addition to SARS-CoV-2 may be required in the search for a correct diagnosis. The analysis results from these tests are also available for patients who log onto helsenorge.no. The person ordering the tests should explain to the patient what they are being tested for." 

17.09.2020: Updated flowchart and added link to the PDF version.

15.09.2020: Estimate for specificity changed from 99.9% to 99.999% in text and figures.

04.09.2020: Added "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."

28.08.2020: Updated flow chart on interpreting COVID-19 test results. Fact sheet updated with that you should stay at home until a negative COVID-19 test result is available and you are in good general condition. Added paragraph about waiting for test results.

27.08.2020: Changed from "The doctor at the test centre is responsible for informing the patient and their regular doctor of the test result, and for notifying the Norwegian Surveillance System for Communicable Diseases (MSIS) of any positive results on the same day they are available" to "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." 
Added "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".   

Updated * and ** in the first flow chart - from "children under 10 years" and "symptom-free to *Children of primary school/ child care age who only have a runny nose and are in general good health without other symptoms of new respiratory tract infection do not need to stay at home.**For children of primary school/ child care age who have mild symptoms, observe the symptoms at home before testing. If they recover quickly, they can return to school / child care without being tested.

20.08.2020: Moved the sentence "Anyone who suspects that they have COVID-19 should have the opportunity to be tested" to point number 4 in the list over who should be tested.

15.08.2020: Clarified responsibility around sending in MSIS notifications. Clarified advice about testing upon arrival from regions (not areas) with high incidence.

13.08.2020: Changed point 2 in supplementary information about who should be tested - removed distinction between "household members and equivalent close contacts" and "other close contacts".

12.08.2020: Test criteria updated as per Norwegian version.

31.07.2020: Added to the text box: People returning from countries which, after their return, were categorised as "red" should be given priority for testing (Norwegian Government decision of 23 July 2020).

23.07.2020: Added section of interpretation of positive PCR test results after disease review.

20.07.2020: Added a new point that Health personnel, who will work close to the patient, within 10 days after a trip abroad to "green countries", can be considered tested even if they are asymptomatic. And a new point that close contacts who are in quarantine (household members and similar close contacts) can be tested to hasten further infection tracking, if the laboratory capacity allows it.

17.07.2020: Added a point that Health personnel who will work close to the patient within 10 days after a trip abroad to «green countries», should be tested even if they are asymptomatic.

03.07.2020: Updated flowcharts. Changed "new respiratory tract infection infection" to "newly arisen respiratory tract infection. 

01.07.2020: Added section: COVID-19-related test results at helsenorge.no and in Summary care records

29.06.2020: Updated flowchart for COVID-19 testing. Emphasised that newly arisen respiratory tract infections should be tested. Added exemptions for chiildren under 10-years-old.

24.06.2020: Added sentence "Everyone who is tested should stay at home until they get a negative test result AND they are symptom-free" in the section "everyone with symptoms should be tested". Changed sentence about symptoms that are less typical to "With other symptoms that are not typical for COVID-19 among people who do not need medical attention, the symptoms can be observed at home before being considered for testing."

22.06.2020: Adjusted text about test criteria, as per Norwegian version

19.06.2020: Updated who should be tested (first and second paragraphs in body text)

11.06.2020: Added flowchart for interpretation of results

04.06.2020: Added that close contacts who are not going to be quarantined should be tested.

31.05.2020: Added that testing can be an alternative to quarantine. Clarified interpretation of unexpected test results. Removed flowchart that is now incorrect after changes to COVID-19 regulations.

28.05.2020: Added figures 1 and 2.

26.05.2020: Put prioritisation list in a text box, clarified that everyone with symptoms should be tested if capacity is available.

25.05.2020: Updated as per Norwegian version. 

07.05.2020: Updated ingress as per Norwegian version. "It is advised that everyone with suspected COVID-19 should be tested. With limits in testing capacity, the following order of priority is recommended:"

04.05.2020:

Removed "This is why the quarantine period cannot be shortened based on a negative test result" from paragraph about "Why people without symptoms are not tested."

30.04.2020
Removed paragraph about the strategy, as per Norwegian version.

22.04.2020

Added ****Should preferably monitor symptoms at home for 2 days before considering testing.

20.04.2020

Changes as per Norwegian text. Changed paragraph about prioritised indications for testing of COVID-19. Added sentence "People with acute respiratory tract infections with fever, cough or breathing difficulties, or who a doctor suspects has COVID-19" over list of prioritised groups.

17.04.2020
Updated point 4 as per Norwegian text and changed some of the diseases under ***

12.04.2020
Added "With a negative test result but strong clinical suspicion of COVID-19, consider re-testing."

05.03.2020
Clarification - if there is good capacity, it is recommended to test everyone with symptoms that could be due to COVID-19, particularly with admission.

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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.