More than two-thirds of the people in the slum areas of Dhaka and Chattagram have most definitely been exposed to Covid-19, found a study by the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b).

About 72 percent of the samples collected from those in slum areas by the study had antibodies, which indicate exposure to a SARS-CoV-2 (COVID-19) infection.

Antibodies are proteins made by the immune system to fight infections like viruses and may help to ward off future occurrences by those same infections. It can take days or weeks to develop in the body and it is unknown how long they stay in the blood.

The study titled "Driving factors of COVID-19 in Slums and Non-slum Areas of Dhaka and Chattogram" was conducted between October last year and February this year to evaluate the extent of the spread of SARS-CoV-2 infection in the slum and non-slum communities of the two cities.

A cross-sectional study was carried out among 3,220 people residing in the slums and the adjacent non-slum areas in the two cities. Household-level interviews, blood pressure and anthropometric measurements, and blood samples were collected and a seroprevalence survey carried out.

A seroprevalence survey uses antibody tests to estimate the percentage of people in a population who have antibodies against SARS-CoV-2.

The estimated SARS-CoV-2 antibody seroprevalence was higher in slums than in the adjacent low-to-middle-income non-slum areas, said the study, which was unveiled at a webinar yesterday. Rubhana Raqib, the principal investigator of the study, presented the study findings.

The overall seropositivity, which means having the presence of antibodies in blood serum, was higher in Dhaka than in Chittagong: 71 percent as opposed to 55 percent in the port city.

It also found that the presence of antibody is almost similar across the adults and the young.

The seroprevalence was higher in females (70.6 percent) than in males (66 percent), it said.

Among the people whose antibody was found, only 35.5 percent were estimated to have some/mild symptoms, the report finds.

"Since the young and working-class people live in the slum areas, probably that explains why they got some sort of protection from the severity of the covid-19 infection," said Mahmudur Rahman, chair of the executive advisory committee of the study.

The study samples are purposive, so they would not represent the whole scenario of the country.

"This study will help to predict the future situation and such studies should be done more frequently to track the trend of the Covid-19 situation."

Stressing on mask wear, Rahman, a former director of IEDCR, said the face-covering protects against all variants.

A higher prevalence of antibody was found in individuals with fewer years of education, diabetes, overweight and hypertension.

Lower antibody was found in individuals who frequently washed hands, did not put fingers on the face/in the nose, have been vaccinated with BCG and carried out moderate physical activities.

The level of zinc was higher in the seropositive individuals than the seronegative ones.

This may be related to mild disease or asymptomatic infection in the study population, finds the study.

Inadequate vitamin D status did not show any impact on seropositivity. Rather, there was a high rate of vitamin D insufficiency in the population.

"We need to keep continuing the vaccination and research to understand the situation -- the situation is changing and so the research must be ongoing to understand the trend," said Firdausi Qadri, senior scientist at icddr,b.

The study does not reflect the severity of the disease, said Tahmeed Ahmed, executive director of icddr,b.

Physical activity should be increased and preventive measures like wearing masks, maintaining social distancing should be strictly followed.

If people have any of the three symptoms -- fever, coughing and sore throat -- they should be tested.