As Poslovni Dnevnik writes on the 11th of May, 2020, the ELISA test is a method of serological diagnosis that detects certain classes of antibodies, IgM, IgG and IgA in the patient's serum. The first serological testing to see just how many of Croatia's residents have actually been infected with the new coronavirus, perhaps without ever knowing, has now begun.

The Croatian Institute of Public Health (HZJZ) has started coronavirus serological testing which should provide us with a long-awaited answer about the prevalence of coronavirus in the population of Croatia, ie, what percentage of Croatia's residents have been infected, perhaps asymptomatically. Serological testing includes 1,100 blood samples from citizens collected from hospital laboratories, health centres and public health institutes.

''So far, as part of the validation of these tests, in addition to serum samples from patients who have been confirmed to have had a coronavirus infection, we've also tested 120 people from the general population and healthcare professionals with the ELISA test. Based on such a small number of respondents, it's currently much too early to talk about the prevalence of coronavirus among the general population. As announced by the director of the CNIPH, Dr. Krunoslav Capak, this week, we'll begin testing a larger number of respondents, which will allow for us to gain a better insight into the level of infection of our population,'' said Dr. Tatjana Vilibic-Cavlek, head of the Department of Virological Serology of the CIPH, for Jutarnji list.

''The ELISA test is a method of serological diagnosis which proves the presence of certain classes of antibodies, IgM, IgG and IgA, in the patient's serum. Depending on the proven antibodies, we can tell if it they've had an acute or recent infection, or if they've had earlier contact with the virus. If a person has antibodies to SARS-CoV-2, it means that they have acquired immunity, but we don't know much more about the duration of that immunity because this coronavirus is a brand new virus and too little time has passed since its appearance to talk about long-term immunity,'' she added.

Serological tests are also being conducted in other European Union countries, and results from the Czech Republic and neighbouring Slovenia show that between two and five percent of the population have been infected with the new coronavirus in those countries.

In the event that something of a similar result here in Croatia, it would, according to estimates, mean that a maximum of 125,000 Croatian residents have been infected, which is certainly insufficient to achieve collective immunity (herd immunity), which is between 60 and 70 percent in the case of the new coronavirus. That is, for the SARS-CoV-2 coronavirus to stop spreading among a population, its infection rate must be between 60 and 70 percent.

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As Poslovni Dnevnik writes on the 9th of May, 2020, these coronavirus serological test results could be an important guideline for national-level testing because they give at least a rough picture of how many residents of Croatia have been exposed to coronavirus and got over it without even knowing they'd ever contracted it.

Slobodna Dalmacija has found out that a large number of DIV Group employees were tested last month, including those employed in the Split shipyard. Many people who contract coronavirus are asymptomatic, not realising they are even harbouring the virus. As such, and as previously stated, the results of this serological testing could act as an important guideline for national testing because they provide us with at least a rough picture of how many people have actually contracted it without becoming unwell or being any the wiser.

“In cooperation with the University Department of Forensic Sciences of the University of Split, from April the 23rd to the 28th, we conducted the serological testing of antibodies to 2019-nCoV. 1724 DIV group workers participated in the research, of which 1316 were employees of Brodosplit, which acts as more than a representative sample. During the examination, all GDPR measures were strictly observed, and the coronavirus serological testing was carried out using the AMP Rapid Test SARS-Cov 2 test,'' explained Josip Jurisic, Head of Public Relations of the DIV Group.

The first mass serological testing in Croatia was also commented on prof. Dr. Simun Andjelinovic, professor at the Department of Forensic Sciences at the University of Split.

"We, as scientists, got involved at the invitation of the DIV management to perform this serological testing and scientifically process the results of these tests. What is interesting with these tests is the fact that the infection rate of the tested population is less than two percent. This is a very valuable result, because scientists around the world thought that the prevalence in the population would be much higher.

Such results are the starting point for other coronavirus serological tests, as well as for other preventive measures that will be taken in similar companies and will serve to further develop the system of the safety of workers and their job satisfaction. We'll publish the results of our research in scientific journals and they will be used for all future scientific evaluations of such threats,'' said prof.dr. Andjelinovic.

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As Poslovni Dnevnik writes on the 20th of April, 2020, all citizens who have had their blood drawn since Wednesday for various health check ups unrelated to coronavirus (COVID-19) are potential candidates for conducting a major study to find out just how deeply coronavirus has entered the population, according to a report from Jutarnji list.

''The first phase will see the random selection of 1,100 blood samples, collected from hospital laboratories, health centres and public health institutes from across the country. Croatian labs have been keeping hold of blood samples since Wednesday. The collection will take about ten days, and by then we expect 1100 ELISA tests to arrive, which will determine how many people have developed antibodies, that is, how many, without knowing it, were in contact with the virus,'' Krunoslav Capak, the director of the Croatian Institute of Public Health, whose facility will be carrying out the testing, explained.

''At this stage, these will be ''anonymous'' samples, that is, only the gender of the person, their age and whether or not he or she is suffering from a disease or is completely healthy will be known. The person's first name doesn't matter to us. What we want to do is see how many people actually have had the virus asymptomatically. We chose such samples because we consider them to be the most relevant in terms of representing the population. Some countries have opted to use the blood of voluntary blood donors, but we believe that we wouldn't get a quality picture because most blood donors are healthy, middle-aged men,'' said Capak.

Considering the fact that this coronavirus is new and we're still in the research phase, this kind of study is being done for two reasons. The first reason is, as Capak explained, to see how many asymptomatic cases we have, that is, how many people have contracted the new coronavirus without even knowing it. The other reason is to see how many antibodies have, as such, been developed.

Specifically, it will be possible to monitor how long immunity to the disease lasts over time, which is something that is currently unknown and being questioned.

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