'Silent transmitters' responsible for 50% of virus infections
The influence of presymptomatic and asymptomatic people in the transmission of the SARS-CoV-2 virus, which causes Covid-19 disease, was evidenced in a scientific study published last July 6 in the journal Actas of the National Academy of Sciences from the United States.
The study, led by Alison Galvani of Yale University and her colleagues, indicates that presymptomatic and asymptomatic people are responsible for 50% of infections.
The research used coronavirus transmission models and existing research, which already indicated that asymptomatic infections represent 17.9% to 30.8% of all infections.
Based on these figures, the team made a new transmission model and found that presymptomatic people would represent 47% to 48% of transmission, and asymptomatic people 3.4% to 6.6%.
The document also states that immediate isolation of all symptomatic cases would not be enough to control the spread. Authorities would have to identify and isolate more than a third of the silent transmitters, as well as all symptomatic cases, to prevent an outbreak.
On these findings, Arturo Rebollón, epidemiologist and public health researcher affiliated with Florida State University, said that presymptomatic and asymptomatic patients are detected by following up with rapid antigen tests, and recommended that when the result of an antigen test is negative be verified by other technologies.
This is similar to doing Pap tests to detect uterine cancer, doing mammograms to detect breast cancer, doing the rapid test for HIV or dengue. None of these strategies is 100% effective, but they have a high return on investment due to their low cost and sufficient diagnostic capacity, he explained.
In Panama, little is known about the carriers of the virus without symptoms, but the authorities of the Ministry of Health reported last May that four resident doctors of surgery at the Santo Tomás Hospital became infected with Covid-19 after having contact with patients without symptoms.
The research used coronavirus transmission models and existing research, which already indicated that asymptomatic infections represent 17.9% to 30.8% of all infections.
Based on these figures, the team made a new transmission model and found that presymptomatic people would represent 47% to 48% of transmission, and asymptomatic people 3.4% to 6.6%.
The document also states that immediate isolation of all symptomatic cases would not be enough to control the spread. Authorities would have to identify and isolate more than a third of the silent transmitters, as well as all symptomatic cases, to prevent an outbreak.
On these findings, Arturo Rebollón, epidemiologist and public health researcher affiliated with Florida State University, said that presymptomatic and asymptomatic patients are detected by following up with rapid antigen tests, and recommended that when the result of an antigen test is negative be verified by other technologies.
This is similar to doing Pap tests to detect uterine cancer, doing mammograms to detect breast cancer, doing the rapid test for HIV or dengue. None of these strategies is 100% effective, but they have a high return on investment due to their low cost and sufficient diagnostic capacity, he explained.
In Panama, little is known about the carriers of the virus without symptoms, but the authorities of the Ministry of Health reported last May that four resident doctors of surgery at the Santo Tomás Hospital became infected with Covid-19 after having contact with patients without symptoms.