key: cord-0791808-1zuwb4gt
authors: Ahmed, A.; Rahman, M. M.
title: COVID-19 trend in Bangladesh: deviation from epidemiological model and critical analysis of the possible factors
date: 2020-06-03
journal: nan
DOI: 10.1101/2020.05.31.20118745
sha: 12893aa539717df5ccaa94d15d84cb5c057fcdbf
doc_id: 791808
cord_uid: 1zuwb4gt

Background: Since its first report on March 08, COVID-19 positive cases and number of deaths are increasing in Bangladesh. In the first month of COVID-19 infection, incidence of daily positive cases did follow the susceptible, infected and recovered (SIR) based predictions we reported in April, but started to deviate in the following month. COVID-19 transmission and disease progression depends on multifaceted determinants e.g. viral genetics, host immunity, social distancing, co-morbidity, socio-demographic and environmental parameters. Therefore deviation in confirmed cases from predicted model may appear and warrant thorough investigation. In this short report, we tried to demonstrate and analyze the possible factors associated with the deviation which included preventive intervention strategies, socioeconomic capabilities, climatic and meteorological indexes, acquired immunity of Bangladeshi population, demographic characteristics, health indicators and food habits. Findings: The key factor responsible for the deviation was found to be the number of tests performed. Having population with low median age, young age groups are being mostly infected. Low prevalence of non-communicable diseases among them and strong immunity compared to the elderly might have kept most of them asymptomatic with silent recovery. Warm temperature, humidity and UV index of Bangladesh during this summer period might have contributed to the slow progression of infection. Longer daylight mediated immunity, fresh air circulations and ventilation, less density in rural areas and certain food habits perhaps helped the large number of populations to restrict the infection. Conclusion: Despite all these helpful determinants in Bangladesh, person to person contact is still the leading risk factor for COVID-19 transmission. Infection may increase rapidly if safe distance and preventive measures are not strictly followed while resuming the normal social and work life. A global second wave may hit in many countries in autumn and as well as in Bangladesh in mid-October when winter starts to approach. Strong collaborative action plans, strategies and implementation are needed immediately to prevent catastrophe.

1. Limited number of tests compared to large population was the key reason for possible low daily positive cases reported in Bangladesh. 2. Controlled interventions viz. official leave, transport ban and social distancing had helped initially to slow down the transmission. 3. Warm weather, high humidity and UV index, sunlight mediated immunity, fresh air circulations, low pollutions, food habit and heterologous immunity might have reduced the transmission capabilities of SARS-CoV-2. 4. Having large number of young people with strong immunity might have kept most of the infected asymptomatic who recovered silently. 5. Person to person contact still remain as key risk factor in COVID-19 transmission, so strict health measures should be in place even after reopening social activities to contain further transmission.

Bangladesh is still experiencing daily rise of COVID-19 cases and deaths since its first report on 08 March, 2020. As of 31 May 2020, a total of 47,153 confirmed cases, 9,781 recovery and 650

deaths have been recorded [1] . After its first incidence in Wuhan, China in December 2019, COVID-19 spread to most of countries mostly via international travelers. Bangladesh government initially started with 10 day travel ban across the country from 26 March along with office and educational institutional shut down which was further extended [2] . People were advised to stay home and to maintain social distance, however it was difficult for daily wage earners and for the people staying in very dense premises [3] . During official leave and transport ban some unexpected mass gathering took place including back and forth movement of garments workers to Dhaka, large funeral prayer and crowded journey toward rural areas [1] . But overall the speed of COVID-19 in Bangladesh seemed to be relatively slow.

Susceptible, infected and recovered (SIR) is a classic closed compartment epidemiological model to predict disease trajectory [4] . After the rapid spread of COVID-19 many SIR and modified SIR based prediction have been reported [5] [6] [7] [8] and classic SIR model is claimed to show less complexity and better prediction compared to modified models [9] . These predictions are not always perfectly correct as disease progression is determined by many other factors, however, such predictions help to visualize possible intervention mediated outcomes and action planning can be directed accordingly. In our previous report, we used SIR based prediction of COVID-19

in Bangladesh with different percentage of possible social distancing intervention [5] . Based on another survey and practical scenarios we hypothesized around 60% social distancing could be possible in Bangladesh [10] . In accordance, we showed COVID-19 in Bangladesh might reach . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted June 3, 2020. . https://doi.org/10.1101/2020.05.31.20118745 doi: medRxiv preprint its peak in early June and would be slowed down at the end of August. The daily case number was following our prediction graph very closely till late April. However, after that point confirmed cases did not follow the prediction trend and fell way behind it. As COVID-19 incidence is being controlled by multifaceted parameters, we tried to connect the possible reasons to the ongoing trend of Bangladesh. We considered demographic and climatic parameters, logistic and intervention strategies taken by Bangladesh in coordination with published literature to support the possible reasons.

In this short report, we investigated the deviation pattern of COVID-19 cases from our previously reported SIR prediction model of Bangladesh. We also tried to explain possible reasons behind this deviation and limiting factors in the light of literature. We followed some key events in Bangladesh during this period as well as environmental and behavioral pattern that might have influenced the outcome. In harmony with global scientific data and suggestions we also highlighted the present and future risk factors in Bangladesh which must be addressed to limit rapid progression of COVID-19.

COVID-19 related data of Bangladesh viz. reported daily case numbers, daily test numbers, daily deaths were retrieved on 31 May 2020 [1] . Daily test positive (%) rate, daily percent increase in test numbers and positive cases were calculated and plotted. Findings were compared with our previously reported SIR model and trend of other parameters were analyzed. GraphPad Prism v. 6 .0 was used for plotting and statistical analysis was done with linear and non linear regression.

. CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted June 3, 2020. . https://doi.org/10.1101/2020.05.31.20118745 doi: medRxiv preprint

When we compared previously reported prediction after a month, it was observed that real cumulative cases dropped from the prediction ( Fig. 1 A and B) . The daily test number and positive cases showed linear trend over the period (R 2 =0.9319), but data tend to shift from the straight line as time progressed (Fig. 1 C) . Plotting of predicted vs. real cases showed it deviated from expected straight line to a non linear pattern with tendency of having plateau as rise in real case numbers were slow ( Fig. 1 D) . We also observed that daily percent change in test number and positive cases followed same trend (red and blue line) and with a decline in these values test positive (%) climbed up (shown inside dotted circle) ( Fig. 1 E) . When daily percent deviation of case numbers from predicted values was plotted, it remained mostly negative although a slightly positive trend was observed initially. As days progressed as test numbers became limited the daily deviation followed more negative trend (Fig. 1F ).

. CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted June 3, 2020. . is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted June 3, 2020. . https://doi.org/10.1101/2020.05.31.20118745 doi: medRxiv preprint

To understand the prevalence and distribution pattern of COVID-19, number of tests performed by a country plays critical role. In our previous study, analyzing 91 countries' number of tests performed per 100K population data we found positive as well as negative association with positive cases and test positive (%) respectively with statistical significance [11] . Countries where limited numbers of tests were performed test positive (%) was comparatively higher. We showed that global mean of test positive (%) was 9.94 ± 1.25 and countries with high number of tests (>500 tests per 100K population) had test positive value well below 10% and countries with fewer tests (<500 tests per 100K population) had average test positive rate of about 20% with extreme individual value of 85.51% [12] . Bangladeshi data from last one month showed that daily test positive (%) was increasing with declining daily percent increase in test numbers (Fig.   1E ). This indicated that the test positive (%) was getting higher due to limited number of tests is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted June 3, 2020. . https://doi.org/10.1101/2020.05.31.20118745 doi: medRxiv preprint country which is at present 49 in number. Bangladesh is one of the low investing countries in health sector (health expenditure of 36.28 USD per capita) [13] , thus the extension of test center and recruitment and training of expertise was relatively slow and still way below the need compared to large number of populations. Especially with the increasing rate of infection this can be vital limiting factor to know real case scenario in Bangladesh. These extended centers however are mainly in divisional headquarters or in large cities, where rural people staying away from the facility had difficulty to test as inter-city transport was closed. This has resulted some samples to become non usable and some false negative as samples might have been deteriorated due to longer transport and improper sample collection. We also identified due to social non cooperation toward the COVID-19 positive or health care practitioners, many suspected individual were reluctant to give sample due to social fear. Although government hot line is open for all, many people had dissatisfactory experience calling for sample collection. Lack of management, long queue, waiting time in sample collection and test centers and delayed result also had negative impact, fear and rejection tendency among test seekers. These factors altogether had impact on uniform and broad data collection raising reliability issues on reported case numbers so far.

In our previous report we also found that countries with high median age showed strong association with COVID-19 case fatality rate [11] . This was mainly due to prevalence of non communicable diseases as contributing factor for comorbidity and reduced immunity of elderly people. Bangladesh has median age of 27.90 years [14], with less elderly people. This could be one reason that young age group being dominant in the society are the most infected among all (55% belong to 21 to 40 years age group) [15] . Their inherent strong immunity might be a reason . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted June 3, 2020. 

Scientists are having a wave of optimism that warmer weather might improve COVID-19

scenario [17] . Temperature, absolute humidity, relative humidity (RH), sunlight, ambient air flow, and altitudes were mostly studied parameters [18, 19] . Respiratory viruses usually follow seasonal pattern, preferring either winter or summer, whereas some of them prefer to be year around virus [20] . Information regarding SARS-CoV-2 is still insufficient to label its seasonality; however, known other human corona viruses had shown clear preferences to winter. COVID-19 data so far showed temperate regions as the prevalence hot zone, but tropical areas are not completely out of the list. In one particular season incidence peak or hot spot may vary from virus to virus and usually avoid overlapping. Temperature and humidity determine the route of transmission and viral stability both in indoor and outdoor settings. Cold and dry weather dominate transmission via aerosol and small droplets whereas hot and humid weather facilitate transmission via fomites. Temperature above 30°C showed to block aerosol mediated Influenza virus transmission at variable RH, but contact mode transmission was still possible [21] . Surface stability and viability of SARS-CoV was shown to be lost at high temperature and high RH [22] .

Bangladesh with monthly high temperature above 30°C and average temperature above 25°C . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted June 3, 2020. . https://doi.org/10.1101/2020.05.31.20118745 doi: medRxiv preprint from March to October may have reduced aerosol mediated viral transmission slowing community level infection rate.

UV index and air pollution may also play contributing role in viral transmission. Anthropogenic pollutants and microbes share common mechanism to confer immune deficiency [23] . These pollutants prepare the ground for COVID-19 like pandemic and further worsen the outbreak. Air particulate materials were found to be positively associated with COVID-19 incidence. Due to government imposed travel ban, reduced industrial effect air particulate emission was also low for the last two months which might have helped to reduce particulate material mediated virus transmission. Bangladesh has very high UV index during summer months with average of 10 or above with increased daylight hours [24] . UV index and daylight is related to ozone concentration which was found to reduce viability of viruses and COVID-19 transmission in a study conducted in Chinese cities [25] . In Bangladesh, ozone level in summer daylight may have helped to reduce viability of the viruses in environment [26] . Sunlight exposure which is also related to vitamin D production and immunity had helped to provide population level immunity to fight COVID-19 in Bangladesh [27] . Besides, with official leave, many people left capital city to stay with families in rural areas, where factors like low population density, air velocity, and sunlight exposure were helpful to restrict virus transmission.

Heterologous immunity, a form of cross reactivity is acquired from previously challenged unrelated microorganisms providing wider vaccine induced effectiveness and natural immunity against new infections [28, 29] . Memory CD8+ T cells can help to detect newly infected viruses, but due to strain variation in RNA viruses less effective immunity is observed in human and in some cases show immune pathology [30] . Bangladesh is a densely populated country and people . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted June 3, 2020. . https://doi.org/10.1101/2020.05.31.20118745 doi: medRxiv preprint are exposed to different microorganisms during their lifetime, thus highly likely acquire heterologous immunity from natural infections. One study with cholera vaccination in Bangladesh showed natural immunity were long lasting compared to the oral vaccine [31] . In another study, Bangladeshi children were found to express more effector T cell activity compared to American children, supporting the 'hygiene hypothesis' [32] . According to this hypothesis early exposure to infectious agents may provide better immunity and in contrast lack of exposure may lead to allergies and autoimmune diseases. This also explains in part, reduced COVID-19 incidence in Bangladesh could be due to childhood acquired immunity against a variety of organisms. Co-infection of viruses is another aspect where one or more viruses may compete with another minimizing the virulence of the other [33] . Viral co-infection was reported in COVID-19 [34, 35] and in Bangladesh as viral co-infection was observed in case of other viruses [36] , co-infection of other respiratory viruses may have inhibitory effect on COVID-19 transmission and virulence. Food which boosts immune systems e.g. seasonal fruits, vegetables and spices could also play a positive role in slowing COVID-19 in Bangladesh.

Although many factors seemed to help Bangladesh, other factors like population density, urban population percentage and negligence toward health precautions still pose high risk of person to person disease transmission especially when offices and transport will be open. Climatic parameters may slow down COVID-19 transmission pattern and duration, however considering the size of pandemic its effect is modest [37] . Countries in both temperate and tropical regions must prepare for the possibility of severe outbreak; however, climatic variation will help to determine the local endemic cycle and seasonal peak.

Step by step precautions are necessary to . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted June 3, 2020. . https://doi.org/10.1101/2020.05.31.20118745 doi: medRxiv preprint reduce sudden spike in infection number. Coming winter may face a second wave, so extended measures should be in place to contain the COVID-19 in Bangladesh. Public health policy and strategies need to be carefully adjusted considering these aspects to slow down the pandemic pace so that effective medical facilities can be provided to maximum possible people using available resources.

Ethics approval and consent to participate: not applicable Availability of data and material: secondary data used and cited in this study are publicly available.

Competing interests: authors declare no competing interests. . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted June 3, 2020. . https://doi.org/10.1101/2020.05.31.20118745 doi: medRxiv preprint

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Authors' contributions: AA conceived the idea; AA and MMR equally contributed to the manuscript and agreed to submit in its current form after necessary corrections.