The IEDCR and partners share insights on the prevalence, seroprevalence and genomic epidemiology of COVID-19 in Dhaka city

Dhaka, October 12, 2020: The Institute of Epidemiology Disease Control And Research (IEDCR), in collaboration with icddr,b and the United States Agency for International Development (USAID), organised a dissemination seminar this afternoon on preliminary findings on the prevalence, seroprevalence, and genomic epidemiology of COVID-19 in Dhaka at Lakeshore Hotel, Dhaka.

The Honourable Minister Zahid Maleque MP, Ministry of Health and Family Welfare (MoHFW) graced the seminar as the Chief Guest and was connected via online, while Professor Meerjady Sabrina Flora, Additional Director General, DGHS Directorate General of Health Services (DGHS) and Dr Tahmeed Ahmed, Acting Executive Director and Senior Director, Nutrition and Clinical Services at icddr,b among others were present at the seminar. The USAID’s Deputy Mission director, John Allelo joined the event virtually as a special guest.

In the dissemination, Dr Mahbubur Rahman, from the IEDCR presented the study design and findings of the first part of the study on transmission dynamics to understand the prevalence of COVID-19 infection.

Prevalence of COVID-19 in Dhaka City findings

• Between April 18 and July 5, 2020, the prevalence of COVID-19 was found to be 9.8% on the day of the sample collection. This implies that one in ten individuals were tested COVID positive in Dhaka City.
• The prevalence of COVID-19 cases was highest among the elderly age 60 and over (24%) followed by adolescents age 15-19 years (18%).
• There was no notable difference between the prevalence of COVID-19 cases among the female and male population.
• The prevalence of COVID-19 in Dhaka slums was 5.7% compared to 9.8% in Dhaka city.
• Among COVID-19 positive cases, 82% were asymptomatic, 6% symptomatic and 12% presymptomatic.
• Among the patients who had symptoms, only 15% needed hospitalization. The estimated hospitalization rate among all COVID-19 cases was 1%. Only one death was reported among the study population.

Professor Flora concluded that prevalence of asymptomatic infection is very high, and in order to break the transmission cycle, everyone must wear a mask, maintain physical distancing and proper hygiene practices.

Dr. Firdausi Qadri, Senior Scientist at icddr,b presented on the second part of the study which aims to understand the seroprevalence of the disease and the percentage of people in Dhaka city who had developed antibodies against SARS-CoV-2.

Seroprevalence of COVID-19 in Dhaka findings:

• In Dhaka city, the seroprevalence of IgG and/or IgM was 45% while in the selected slums it was 74%.
• This indicates that by July 2020, 45% of Dhaka city's population had already been exposed to the infection while the exposure was 74% in the slums.
• Seroprevalence does not necessarily mean protection against the virus since there is no consensus on the appropriate threshold level of antibody that can confer protective immunity.

Dr Qadri concluded that the exposure to SARS-CoV-2 has occurred in the study areas. Encouraging rates of seropositivity among the study population of Dhaka city indicates that we have started developing herd immunity against SARS-CoV-2.

Professor Tahmina Shirin, Director, IEDCR presented on the genomic epidemiology of SARS-CoV-2 in Bangladesh, The genomic epidemiology of SARS-CoV-2 in Bangladesh aimed to track the origin, mutation and changes that have occurred in the SARS-CoV-2 strains in Bangladesh. It also looked at COVID-19 spread in the country along with the lineage relationship with global SARS-CoV-2 strains.

In the study, genome sequencing of 67 SARS-CoV-2 strains were completed and compared with 325 sequenced data available in Bangladesh. For phylogenetic analysis, 68,000 whole-length, high-quality GISAID genomes from the rest of the world were also used.

Genomic epidemiology of SARS-CoV-2 in Bangladesh findings

• Findings suggest that SARS-CoV-2 was first introduced to Bangladesh in mid-February 2020
• The main spread happened in March correlating with the mass migration evidenced by the mobility data
• Lineages circulating in Bangladesh are closely related to those circulating globally suggesting therapeutics and vaccine would be just as likely to be effective in Bangladesh as elsewhere in the world
• The mutation in Bangladesh is consistent with the global trend. The mutation rate of SARS-CoV-2 in Bangladesh was estimated to be 0.7 x 10-3 substitutions per nucleotide per year which is consistent with the global SARS-COV-2 estimated mutation rate (0.8 x 10-3).

Prof Tahmina Shirin concluded that study findings show the epidemiologic and phylogenetic findings of SARS-CoV-2 in Bangladesh are consistent with the findings around the globe. This potentially suggests that therapeutics and vaccines that are becoming globally available will be equally effective in Bangladesh.

The Honourable Minister Zahid Maleque MP appreciated the initiatives in his remarks. He said, “Bangladesh did well in preparing against Covid-19 and that helped lower the severity of the virus.” Speaking on the occasion Mr Allelo said, “the findings from the seroprevalence and genomic epidemiology study of COVID-19 in Bangladesh we heard about today are very crucial. These findings offer us an opportunity to carefully review the evidence and develop strategies to fight COVID-19 in a more effective manner.”

National and international public health experts, representatives from the MoHFW, DGHS, IEDCR, UNICEF, USAID, icddr,b, Bill & Melinda Gates Foundations (BMGF) and media were also present at the seminar among others.

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Note to Editor

About the prevalence and seroprevalence study

The Institute of Epidemiology Diseases Control and Research (IEDCR) conducted a national level survey to assess the COVID-19 situation in Bangladesh through icddr,b; with the support of the United States Agency for International Development (USAID) and Bill and Melinda Gates Foundation (BMGF). This is the first national level cross sectional study in Bangladesh that started from April 2020 and is still ongoing. Due to the time sensitivity and importance of data, the study results will be shared in phases. This phase will cover the data from Dhaka city and the rest of the country will be shared by early November, 2020.

To assess the prevalence and seroprevalence of COVID-19 in Dhaka city, a total of 25 wards were randomly selected out of the 129 wards and one mahalla was randomly selected from each ward and from each mahalla randomly 120 households were selected. To assess the situation in the slum, additional eight slums were also included in the survey. The households were categorized as symptomatic and asymptomatic based on the initial screening. If any household members had any of the four COVID-19 symptoms (fever, cough, sore throat, breathing difficulties) on the day of the survey or within 7 days preceding the survey, the household was considered as a ‘symptomatic’ household. If none of the household members had any of the four COVID-19 symptoms on the day of the survey and within the 7 days preceding the survey, the household was considered as an asymptomatic household. All members of symptomatic households and approximately every tenth asymptomatic household were selected for (i) COVID test using Real Time Polymerase Chain Reaction (RT-PCR) and (ii) blood test to detect antibodies.

By seroprevalence we are referring to the presence of antibodies against COVID-19 virus in the blood. Antibody is an essential component of the immune system which helps to protect against diseases and can also neutralize the pathogen. Seroprevalence studies give an idea on the spread of the infection in the community as well as the onset of herd immunity. In this serosurvey, two kinds or isotypes of antibodies were studied- Immunoglobulin M (IgM) and Immunoglobulin G (IgG). The IgM appears first after infection and has a short life span of about 14 days while IgG can last several months after infection in infections including COVID-19.

Blood samples were collected at the time of the interview and serum was separated from blood to detect the antibody level. The enzyme-linked immunosorbent assay (ELISA) procedure was used to determine IgG and IgM antibodies against COVID-19 specific antigen.

About the genomic epidemiology of SARS-CoV-2 in Bangladesh study

The main objective of the genomic component of the study was to determine the phylo dynamics and transmission pattern of SARS-CoV-2 in Bangladesh and to understand the lineage relationship with global SARS-CoV-2 strains. The study team has sequenced complete genomes of 67 SARS-CoV-2 isolates collected between March 8, 2020 to July 5, 2020 by MinION nanopore sequencing and combined this dataset with additional 325 genomes from Bangladesh available at GISAID (www.gisaid.org) as of August 2020. The team then additionally analysed population mobility (a2i from GoB) measured from mobile operators, including Facebook and all four mobile operators and combined this data to the genomics data in the analysis. For phylogenetic context, the team used 68,000 whole-length, high-quality GISAID genomes from the rest of the world.

The genomic epidemiology was implemented by IEDCR in collaboration with icddr,b and ideSHi and was supported by the Wellcome Sanger Institute, UK; University of Bath – Harvard, USA and a2i, Government of Bangladesh.

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