COVID19 Immunity Test

Since the outbreak of covid19 there has been rapid explosion of covid testing kits and confusion can arise with different types of testing available.

In fact, all test types can be utilized in diagnosis, management and following up of covid19 infections. What is suitable for use in one setting cannot be easily applied to another without looking at local circumstances and reason for use of the testing method.

Let's look at these tests, 

PCR TEsting (Gene Xpert)

PCR testing is used to identify presence of virus at the time of testing. It looks for gene of covid19 virus as a sign of presence of covid19 virus and confirms that you are infected when it is positive. This test is widely accepted and done by taking nose swab.

It cannot tell you if you had past infection or had immunity to covid19 infection.

It's expensive test utilizes special equipment and can only be done by trained person in laboratories. It can't be done in most rural settings.

Rapid Covid19 Antigen Test

This test is also done via nose swab and looks for specific covid19 proteins as indication of presence of covid19 virus at the time of testing. Positive test indicates you are infected and potentially can pass the virus to others. It does not tell you if you had virus in the past or you have immunity.

This testing method is easy to do and can be used in rural settings with minimal training unlike PCR test.

Blood antibody Test

Blood antibody test is more recent addition, hundreds of kits with varying usefulness (sensivitity & specificity). There are two types of antibody test available. IgG and IgM antibody tests.

Antibody is what you produce to fight against the covid19 virus and therefore one of the indication for your immunity. We often make IgM antibody in the first 1-2 weeks and after that there is a process called antibody class-switch,  in which we make IgG to fight covid infection.

Hence, positive IgM is an indication of recent covid19 infection and IgG is sign of past infection. In fact, positive IgG indicates that you came across Covid19 some time before. You may have had mild complaints and didn't know about it. Positive IgG can also be seen after covid19 vaccination and indicates that you are now protected.

If you had vaccination and test negative for IgG, then it could mean that you haven't developed immunity despite your vaccination.

Antibody test is also available as rapid test kits.

-------------------

COVID 19 OR CORONAVIRUS INFECTION OR SARS-COV2

Question 1. What is Coronavirus or COVID 19? 

The COVID 19 is an RNA virus that has attracted interest worldwide as recently because it has developed into pandemic and has killed thousands worldwide and shut down economies of the world. It has definitely opened our eyes and changed the way we view the world in how we deal with infectious disease in many ways.

There are so much unanswered questions on COVID 19 virus and the diseases it causes. Whilst this book is limited to addressing diagnosis-related questions only, there is even little we know about the tests we use to pick up this virus in clinical samples.

OVID-19 is a coronavirus also known as called SARS-CoV-2. Coronaviruses belong to a large family of viruses that are common and infect humans as well as many different species of animals, including camels, cattle, cats, and bats.  Rarely, animal coronaviruses can infect humans and then spread between persons. Animal to human transmission occurred with MERS-CoV and SARS-CoV, and now with the virus that causes COVID-19. The COVID19 is a beta-coronavirus, like MERS-CoV and SARS-CoV. All three of these viruses have their origins traced to bats. The genetic sequences of COVID19 from U.S. patients are similar to the one that China initially posted, suggesting a likely single, recent emergence of this virus from an animal reservoir. However, the exact source of this virus is still speculative.

On February 11, 2020 the World Health Organization announced an official name for the disease that has caused the 2019 novel coronavirus outbreak which was first identified in Wuhan province, China. The new name of this disease is abbreviated as COVID19 or coronavirus disease 2019. In the COVID-19, ‘CO’ stands for ‘corona,’ ‘VI’ for ‘virus,’ and ‘D’ for disease. Formerly, this disease was referred to as “2019 novel coronavirus” or “2019-nCoV”.

There are many types of human coronaviruses including some that commonly cause mild upper-respiratory tract illnesses. COVID-19 is a new disease, caused by a novel (or new) coronavirus that has not previously been seen in humans. The name of this disease was selected following the World Health Organization (WHO) best practice for naming of new human infectious diseases.

Question 2. Where did coronavirus originate?

The origin of COVID-19 is still hotly debated topic. It was first reported in Wuhan Province, China. An initial genetic analysis of virus genes seems to indicate that the virus resembles genetics of virus in nature that infects wild bats. Although, animal to human transmission of viruses are rare, COVID-19 is one of first viruses shown not only to infect humans from animal but also has ability to transfer from one human to another after acquiring from bat as a possible host.

Question 3. How dangerous is COVID 19 infection?

Covid 19 infection has killed thousands of people over the last 6 months since it was first reported in Wuhan Province, China December 2019. The mortality rate is reported as 2-6 %. i.e., for every 100 people infected, 2-6 people will die. Compare this to common annual flu virus that has kills only less than 0.1% of infected population.  So it is a very serious disease that kills a lot of people although in PNG we have been very lucky so far to have lost no one person since the last reported case.  At the time of writing at May 2020, PNG has reported only 8 confirmed cases with no deaths.

On a good note, 90% of people do not show signs of infection or only develop mild disease. 

Question 4. What are the signs that I have covid-19 infection?

People infected with COVID 19 have reported wide range of symptoms.  Symptoms appear between 2-14 days after infection. These may include the following;

    Cough

    Shortness of breath or difficulty breathing

    Fever

    Chills

    Muscle pain

    Sore throat

    New loss of taste or smell

Children have milder symptoms than adults. We do not know much about the disease and more and more diseases or presentations are been reported including more recently multisystem inflammatory disease in children or Kawasaki disease.

Question 5. How is it spread?

COVID19 is spread via air droplets expelled during coughing, sneezing, shouting or simple conversation at short distance. In theory, it could also be picked up and unconsciously rubbed into nose or mouth after touching contaminated surfaces.

Question 6. How is it prevented?

Simple hygiene measures as hand-washing, use of face masks, avoiding contact with positive or symptomatic patients and keep distance of at least 1.5metetrs from each other have been proven methods for preventing COVID19 infection. COVID19 can also be controlled by vaccination. The discussion on vaccination is outside the scope of this discussion but various vaccines are available to choose.

Question 7. How is COVID 19 treated?

Evidences of effective treatments available are still emerging. Various drugs used in treatment with varying successes include hydroxychloroquine, dexamethasone, zinc, butasonide, and remdesivir.

Question 8. How is COVID19 infection detected?

Evidence of covid19 is by doing PCR test looking for COVI19 genes using nose or throat swab. Occasionally antibody tests looking of antibody IgM and IgG against COVOD19 can be done.

Question 9. What does Positive COVID19 PCR Test Mean?

Any discussion on lab test and how it’s done and so forth are too technical. In short, positive PCR test means virus is present in your body. It indicates that the person has the virus on the surface of body where the swab was taken; usually inside the nose for COVID19.

Question 10. Does Positive PCR COVID19 test mean that I am infected?

By strict definition, infection is defined as inflammation or tissue reactions and accompanying chemical changes or tissue damage occurring with invasion or contact with an infectious organisms and resulting disease. Whether or not COVID19 causes infection or disease depends on your body’s immune system. The signs and symptoms that an infected person display reflects a disease process occurring as a result of immune or inflammatory reaction that develops in response to COVID19 virus invasion.

Hence, if you are only positive to PCR test but do not have symptoms or signs (of infection) you aren’t infected and have no disease. The virus is only transiently or temporarily in contact with your body without causing disease. In other words, you are only carrying the virus and have no infection. Alternatively, positive test without signs of infection may also occur in early stage of COVID19 infection.

On the other hand, if you are positive for PCR and you also have signs and symptoms of COVID19 infection, then you are infected.

Question 11. What does Negative COVID19 PCR Test Mean?

Negative PCR test indicates that COVID19 virus is absent from you and you are unlikely to get infected. Negative test can also occur if you were infected but cleared the virus from your body already.

Question 12. Can you get false positive or false negative PCR test?

The PCR technology is well designed these days that false test results are uncommon. However, your doctor will recheck your test if there is any doubt on the results reported.

Ideally, combined results of tests done in two different laboratories or another test based on antibody test will increase the confidence of test results obtained. This is more important for people without signs and symptoms of COVID-19 infection.

Question 13. How does positive antibody test mean?

Raised or Positive IgM is seen in person who has active infection or was recently infected, usually in the last 10 days. Positive IgG is seen in person who has had past (natural) infection and is now immune or person who has had vaccination.

 If your IgG is negative after vaccination, than you are not protected and have not developed immunity to the vaccine given. In other words, you need another dose of vaccine.

14. Why do people die after COVID 19 Vaccination?