infectious diseases
COVID 19
Diagnosis of COVID 19
Real-time reverse transcriptase–polymerase chain reaction (RT-PCR) or other nucleic acid amplification test (NAAT) of upper and lower respiratory secretions Antigen testing of upper respiratory secretions The following people should be tested for COVID-19: People with Symptoms and Signs —isolation is recommended until negative test results are received People who have been in close contact with a COVID-19-infected person but are asymptomatic—get tested at least 5 days after exposure; wearing a mask is recommended until negative test results are received People asked to test because of school, workplace, health care setting, government requirements, or other scenarios such as indoor events People who took part in activities that put them at higher risk for COVID-19, such as attending large social gatherings or being in crowded indoor settings without correct and consistent masking, may also want to be tested. Diagnostic testing for COVID-19 is available through laboratories and public testing sites and can also be done at home. There are two main types of diagnostic COVID-19 tests: real-time reverse transcriptase–polymerase chain reaction (RT-PCR) (or other nucleic acid amplification test [NAAT]) and antigen tests. The choice of diagnostic test and its interpretation should be influenced by the likelihood of the person having COVID-19 based on the prevalence of SARS-CoV-2 in the population and the presence of COVID-19 symptoms, signs, or close contact with a known case of COVID-19. RT-PCR has the highest analytical sensitivity and specificity and is the gold standard diagnostic test for COVID-19. Other NAAT platforms are generally slightly less sensitive than RT-PCR with equivalent specificity (seeCDC: Nucleic Acid Amplification Tests). Positive viral PCR tests, however, do not always indicate active infection. They can detect nonviable viral nucleic acid fragments and may remain positive for at least 3 months after initial diagnosis regardless of symptoms. ). This can be an important measure to identify asymptomatic cases and interrupt SARS-CoV-2 transmission. Point-of-care or home-based antigen detection tests are less sensitive than NAATs, particularly at the onset of infection when viral load may be lower. The sensitivity of these tests compared to PCR tests vary by manufacturer and time course of infection, with ranges reported from 40 to 90% ( Diagnosis references ). Therefore, it may be necessary to confirm some antigen test results (eg, a negative test in a person with symptoms) with an RT-PCR or other NAAT. Many antigen-detection test kits also recommend repeating the test serially over several days to increase the likelihood of detecting infection (see also Acceptable specimens for COVID-19 diagnostic testing include nasopharyngeal, oropharyngeal, nasal mid-turbinate, anterior nares, and saliva. Refer to the accepting laboratory's collection instructions or test kit package insert instructions, because not all testing platforms and laboratories may be able to test all specimen types. These may be collected by a health care practitioner or self-collected, with the exception of nasopharyngeal specimens, which should only be collected by an appropriately trained and credentialed health care practitioner. For nasopharyngeal and oropharyngeal specimens, use only synthetic fiber swabs with plastic or wire shafts. Do not use calcium alginate swabs or swabs with wooden shafts, as they may contain substances that inactivate some viruses and inhibit PCR testing. The swabs should be placed immediately into the transport tube provided. Maintain proper infection control when collecting specimens. For biosafety reasons, local institutions and laboratories should not attempt to isolate the virus in cell culture. Positive test results done in a laboratory or health care setting are reported to local and state health departments. Some local health departments also have mechanisms for reporting positive at home test results. Serologic, or antibody, testing should not be used to diagnose acute COVID-19 illness, because antibodies most commonly become detectable only 1 to 3 weeks after symptom onset. Antibody tests are available that target the SARS-CoV-2 nucleocapsid antigen, spike antigen, and the receptor binding domain of the spike antigen. Tests that detect antibody to the nucleocapsid protein are recommended to evaluate for evidence of prior infection in vaccinated persons as that antigen is not included in the vaccine. Quantitative and semi-quantitative antibody assays are available, but there is currently no accepted correlate of immunity, and testing is not recommended to determine immune response to vaccination or infection (seeCDC: Interim Guidelines for COVID-19 Antibody Testing). Routine laboratory findings for those with more severe disease include lymphopenia as well as less specific findings of elevated aminotransaminase (ALT, AST) levels, elevated lactate dehydrogenase (LDH) levels, D-dimer, ferritin, and elevated inflammatory markers such as C-reactive protein. Patients with dyspnea, hypoxia on home oximetry, or other concerning symptoms should be referred for in-person medical evaluation, including oxygen saturation measurement, and followed up with for signs of clinical deterioration. Chest imaging findings can be normal with mild disease and increase with increasing severity of the illness. Typical findings are consistent with viral pneumonia and include ground-glass opacities and consolidation on either chest x-ray or chest CT. Chest imaging is not recommended as a routine screening tool for COVID-19. 1.Drain PK: Rapid diagnostic testing for SARS-CoV-2.N Engl J Med386(3):264-272, 2022. doi: 10.1056/NEJMcp2117115 2.Ford L, Lee C, Pray IW, et al: Epidemiologic characteristics associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen-based test results, real-time reverse transcription polymerase chain reaction (rRT-PCR) cycle threshold values, subgenomic RNA, and viral culture results from university testing.Clin Infect Dis73(6):e1348-e1355, 2021. doi: 10.1093/cid/ciab303 3.Wu S, Archuleta S, Lim SM, et al: Serial antigen rapid testing in staff of a large acute hospital.Lancet Infect Dis22(1):14-15, 2022. doi: 10.1016/S1473-3099(21)00723-4 4.Dinnes J, Sharma P, Berhane S: Rapid, point-of-care antigen tests for diagnosis of SARS-CoV-2 infection.Cochrane Database Sys RevJuly 22, 2022. doi: 10.1002/14651858.CD013705.pub3/full 