June 1, 2023

The City of Baguio has started using the rapid antigen test as a mode of testing for Covid-19 in certain instances after the Inter-Agency Task Force for the Management of Emerging Infectious Diseases adopted the protocols on its pilot use in the city.
IATF Resolution 73 issued Sept. 22 has allowed the city government to test the antigen testing in two instances. First, it should be used among contacts of confirmed Covid-19 cases in areas where there are documented clustering of cases, and second, for domestic tourists and visitors with essential travel, as agreed upon by the city government and the Department of Health with the guidance from DOH expert groups. 
The IATF also enjoined the DOH, Department of Tourism, and World Health Organization to continue providing assistance to the city for the undertaking.
The resolution is in line of the major changes adopted by the IATF in the Covid-19 reclassification method for provinces, highly urbanized cities, and independent component cities and use of new parameters for escalation and de-escalation of community quarantine classification, among others.
City Health Services Office head Rowena Galpo said the city has started using antigen test on Sept. 23 on 167 individuals and 24 of them turned out to be positive for Covid-19.
She clarified the antigen test is being used side-by-side with the RT-PCR or swab test.
“Ito ay ginagawa natin parallel to RT-PCR. Those who we subjected to swab test we also conducted the antigen test at the same time,” Galpo said.  
She said they are also looking into using antigen test on travelers starting Oct. 1 once they come in and also on returning Baguio residents.
She said results of the antigen test can be known in 15 to 30 minutes.
Factors considered in the use of antigen test include cost, as it is less expensive than RT-PCR test; turnaround time, reliability, and availability of test kits.
Galpo said the potential of antigen test in detecting the Covid-19 infection among asymptomatic individuals is still unknown that is why it is being pilot tested in the city.
The antigen is done for free during the pilot test. 
The WHO last week issued a statement which does not recommend the use of antigen test but it can undergo further study. 
Department of Health-Cordillera Director Ruby Constantino said the antigen test is not for asymptomatic individuals because the available antigen tests in the country are not 80 percent sensitive.
She explained for an antigen test to be effective, it must have a sensitivity rate of 80 percent and specifity of 90 percent. 
“If it is below 80 percent sensitive, then it might give a false positive result. However the WHO said to do pilot testing, which is now being allowed in Baguio City,” Constantino said.
If used, antigen should be done by serial testing, or the test must be repeated. 
“For example, when a tourist arrives in the city and they do the antigen test, and then if he or she will stay here longer, (we should) repeat the test on the third or the fifth day according to the WHO guideline. It should not be used only once,” Constantino said.
According to the WHO, antigen as a type of rapid diagnostic test “detects the presence of viral proteins (antigens) expressed by the Covid-19 virus in a sample from the respiratory tract of a person. If the target antigen is present in sufficient concentrations in the sample, it will bind to specific antibodies fixed to a paper strip enclosed in a plastic casing and generate a visually detectable signal, typically within 30 minutes. The antigen detected is expressed only when the virus is actively replicating; therefore such tests are best used to identify acute or early infection.”
The test depends on several factors, and based on experience with antigen-based rapid diagnostic tests for other respiratory diseases such as influenza, the sensitivity of these tests might be expected to vary from 34 to 80 percent, and therefore WHO does not recommend its use for patient care, although research into their performance and potential diagnostic utility is highly encouraged. – Hanna C. Lacsamana