Clinical Diagnosis
The symptoms of COVID-19 remain very similar to those of the other respiratory epidemics in the past, which includes SARS and MERS, but here the range of symptoms includes mild rhinitis to septic shock. Some intestinal disturbances were reported with the other epidemics, but COVID-19 was devoid of such symptoms. When examined, unilateral or bilateral involvement compatible with rival pneumonia is observed in the patients, and bilateral multiple lobular and sub-segmental consolidation areas were observed in patients hospitalized in the intensive care unit. Comorbid patients showed a more severe clinical course than predicted from previous epidemics. Diagnosis of COVID-19 includes the complete history of travel and touch, with laboratory testing. It is more preferable to choose serological screening, which can help to analyze even the asymptomatic infections; several serological tests are in progress for SARS-CoV-2.
Laboratory testing for coronavirus disease 2019 (COVID-19) in suspected human cases
The assessment of the patients with COVID-19 should be based on the clinical features and also epidemiological factors. The screening protocols must be prepared and followed per the native context. Collecting and testing of specimen samples from the suspected individual is considered to be one of the main principles of controlling and managing the outbreak of the disease in a country. The suspected cases must be screened thoroughly in order to detect the virus with the help of nucleic acid amplification tests such as reverse transcription polymerase chain reaction (RT-PCR). If a country or a particular region does not have the facility to test the specimens, the specimens of the suspected individual should be sent to the nearest reference laboratories per the list provided by WHO.
It is also recommended that the suspected patients be tested for another respiratory pathogens by performing the routine laboratory investigation per the local guidelines, mainly to differentiate from other viruses that include influenza virus, parainfluenza virus, adenovirus, respiratory syncytial virus, rhinovirus, human metapneumovirus and SARS coronavirus. It is advisable to distinguish COVID-19 from other pneumonia. Several published pieces of literature based on the novel coronavirus reported in China declared that stool and blood samples can also be collected from the suspected persons in order to detect the virus. However, respiratory samples show better viability in identifying the virus, in comparison with the other specimens.
Nucleic acid amplification tests (NAAT) for COVID-19 virus
The gold standard method of confirming the suspected cases of COVID-19 is carried out by detecting the unique sequences of virus RNA through reverse transcription polymerase chain reaction (RT-PCR) along with nucleic acid sequencing if needed. The various genes of virus identified so far include N, E, S (N: nucleocapsid protein, E: envelope protein gene, S: spike protein gene) and RdRP genes (RNA-dependent RNA polymerase gene).
Serological testing
Serological surveys are also considered to be one of the most effective ones in facilitating outbreak investigation and it also helps us to derive a retrospective assessment of the disease by estimating the attack rate. According to the recent literature, paired serum samples can also help clinicians to diagnose COVID-19 in case of false negative results in NAAT essays. The literature also declared that the commercial and non-commercial serological tests are under consideration in order to support the practicing clinicians by assisting them in diagnosis. Similarly, there are studies published on COVID-19 which are comprised of the serological data on clinical samples.
Viral sequencing
Apart from confirming the presence of virus in the specimens, viral sequencing is also quite useful in monitoring the viral genomic mutations, which plays a very significant role in influencing the performance of the medical countermeasures inclusive of the diagnostic test. Genomic sequencing of the virus can also help further in developing several studies related to molecular epidemiology.
Specimen collection and storage
A Nasopharyngeal and oropharyngeal swab should be collected using Dacron and polyester flocked swabs. It should be transported to the laboratory at a temperature of 4℃ and stored in the laboratory between 4 and -70℃ on the basis of the number and, in order to increase the viral load, both nasopharyngeal and oropharyngeal swabs should be placed in the same tube. Broncho alveolar lavage and nasopharyngeal aspirate should be collected in a sterile container and transported similarly to the laboratory by maintaining a temperature of 4℃.
Sputum samples, especially from the lower respiratory track, should be collected with the help of sterile container and stored, whereas tissue from a biopsy or autopsy should be collected using a sterile container along with saline. However, both should be stored in the laboratory at a temperature that ranges between 4 and -70℃. Whole blood for detecting an antigen, particularly in the first week of illness, should be collected in a collecting tube and stored in the laboratory between 4 and -70℃. Urine samples must also be collected using a sterile container and stored in the laboratory at a temperature that ranges between 4 and -70℃.