{"id":101219,"date":"2020-04-16T16:38:52","date_gmt":"2020-04-16T23:38:52","guid":{"rendered":"http:\/\/www.lankaweb.com\/news\/items\/?p=101219"},"modified":"2020-04-16T16:38:52","modified_gmt":"2020-04-16T23:38:52","slug":"the-evolution-of-the-covid-19-in-sri-lanka-and-prospects-for-relaxing-many-constraints","status":"publish","type":"post","link":"https:\/\/www.lankaweb.com\/news\/items\/2020\/04\/16\/the-evolution-of-the-covid-19-in-sri-lanka-and-prospects-for-relaxing-many-constraints\/","title":{"rendered":"The evolution of the Covid-19 in Sri Lanka and prospects for relaxing many constraints."},"content":{"rendered":"

By Chandre Dharmawardana<\/em><\/span><\/h2>\n\n\n

[This is a\nshortened version of a more technical paper, 15-04-2020]<\/p>\n\n\n\n

Introduction.<\/strong><\/p>\n\n\n\n

An outbreak of a\nnew type of  pneumonia like disease was\nfirst reported on 31st December 2019 from Wuhan City in the Hubei Province of\nChina. It was identifies as caused by  a\n‘Novel Corona Virus’ on 7th January 2020, and renamed Covid-19 on 11th February\n2020. The WHO  upgraded  the disease to a pandemic on the 11th of\nMarch 2020.<\/p>\n\n\n\n

From then on, many\ncountries all over the world rushed to impose social distancing, lockdowns and\ncurfews to prevent the spread of the disease. Sri Lanka’s initial official  response to Covid-19 began on January 27 when\nquarantine measures were imposed on incoming air passengers.   The first local case, a guide working with\nItalian tourists,  was detected on 10th\nMarch, and the importance of methodically identifying transmission chains\nbecame clear. This can be more important than blindly testing populations\nlooking for Covid-19 positive cases (see my article in the Island, 1st April).<\/p>\n\n\n\n

The government at\nfirst attempted to contain the people in their homes by declaring public\nholidays and extending them. However, from March 18th  the government began to impose curfews in\nCovid-19 hot spots, many being in areas to which returnees from abroad,\ntravelers or religious teachers  had\narrived and irresponsibly  ignored  social distancing and quarantine  requirements. \nOther who hold irrational beliefs (e.g., that the disease is caused by\nnon-humans working in consort with Naga beings\u201d) also ignored social\ndistancing, wearing masks etc., and proposed inhaling herbal smoke and\nconsuming broth made from traditional rice\u201d for fighting  the disease!<\/p>\n\n\n\n

In Western\ncountries too,  patterns of transmission\nthrough human chains proved important. Also, \nsupport workers who worked in multiple nursing homes were potential\ncarriers  for  spreading the disease. Nearly half of the\ndead in Canada from Covid-19 are in nursing homes.  Such transmission chains are not normally\nimplemented in  simulation models that\nare used in epidemiology.  Furthermore,\nsome countries, when releasing daily data of “new cases\u201d do not separate\nout cases that appear in quarantined populations from cases that appear from\nwithin the general public. New cases detected in quarantined locations do not\nadd to the growth of the epidemic and should be treated differently in\nepidemiological modeling. What are labeled as “Covid-19 cases\u201d in one\ncountry may not conform to the same labeling in another country.<\/p>\n\n\n\n

Many of the\nepidemiological simulation models in current use are well known in the physical\nsciences and in ecological studies (see Bolker, \nEcological models and data<\/em>. Princeton University Press). They are\napplied to competing chemical reactions, polymerization processes, competing\nplant growth etc. Most  of these\nprocesses begin with a period of exponential growth which gets gradually dampened\nand  flattens out\u201d. That is, many growth\nprocesses that are very different at the “individual level”  all display \ngrowth and saturation characteristics having a universal shape. The so\ncalled logistic model is one of the simplest models belonging to this class.\nHere we exploit this universality and use a more sophisticated version of such\na model to study Sri Lanka’s Covid-19 data.  \n<\/p>\n\n\n\n

Data analysis\nand modeling.<\/strong><\/p>\n\n\n\n

The Epidemiology\nunit of Sri Lanka’s ministry of Health (EU-SLH) has provided authoritative\ndocumentation in  monitoring the evolution\nof Covid-19 via its daily bulletins. The cumulative numbers, i.e., the total\nconfirmed cases” reported by EU-SLH \ndata are displayed in Figure 1 (curve with squares). <\/p>\n\n\n\n

The data from 10th\nof March to 15th April have been used in constructing our epidemiological model\nwhich can be constantly updated as new data comes in. It is clear that the\ntrend in the data changes  from 25th to\n30th March, and then resumes its upward trend though with a different rate. This\nbi-modal characteristic is seen in the daily-change figures as well, in spite\nof the  noisy nature of the data. This\nsuggests two independent loci of infection, or the effect of government\ninterventions to control the epidemic, occurring with a time lag. <\/p>\n\n\n\n

 Efforts have been made to  account for the fact that  the confirmed cases\u201d reported  daily by the EU-SLH includes new cases that\nappear among quarantined  people. If the\nquarantining is effective, such new cases should not push the curve upwards\u201d\nand change the final flattening trend of the curves. For instance, on the 13th\nof April 15 new cases were reported, when the cumulative number of confirmed\ncases jumped from 218 to 233. However, all 15 new cases were from those already\nconfined in quarantine centers, and hence cannot be included as infection loci\nfor the public. A data curve corrected for such cases is given (with triangles)\nin the figure, and labeled confirmed public cases\u201d. Using these sets of data,\nwe give our model results, and predict the long-term behaviour (asymptotic behavior)\nand the number of cases to expect when the curve flattens\u201d, in each scenario.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Figure 1. Models\nfor the time evolution of the total number of Covid-19 cases, showing\nprojected  long-term behaviour for three\ntypes of data treatment.<\/p>\n\n\n\n

If we consider the\ndata set labeled as confirmed public cases\u201d, where Covid-19 cases arising\namong quarantined people are not considered relevant to the spread of the\nepidemic, then the long-time asymptote \nis about 206, and definitely below 210. If all cases (the cumulative\ndaily totals reported by the EU-SLHD) are included in fitting the model, then\nthe projection is 298, and certainly below 310. On the other and, if only the\ninitial data set (prior to the imposition of social distancing and curfews) were\nused, the asymptote  is ~325, but\nalternative parameter choices giving even 600 are possible. This shows that\nsocial distancing and curfews were effective in constraining the evolution of\nthe epidemic.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Figure 2. A\ncomparison of daily new\u201d numbers of the model prediction and actual data.<\/p>\n\n\n\n

The model can now\nbe used to predict the daily new\u201d numbers from<\/p>\n\n\n\n

10th<\/sup>\nMarch onwards, and examine how well they agree with the observed data. Note\nthat what was fitted was the cumulative daily totals, and not this differential\nquantity. Hence good agreement with<\/p>\n\n\n\n

the general trends\nin the daily new\u201d numbers is a useful test of the quality of the model. Our\nmodel reproduces the rough bi-modal character of the observed data and the\ngeneral trends (Fig. 2).<\/p>\n\n\n\n

Conclusion.<\/strong><\/p>\n\n\n\n

 Assuming that that the hospital resources are\nable to handle even 500 cases, these studies suggest that Sri Lanka  should be able to resume nearly normal\neconomic and civic activity by the end of the first week of May, assuming that\nthe epidemic retains the characteristics shown in the current data. The\nconfirmed new cases are arising mainly in \nhotspots in six districts, while the other districts seem  close to normal. Hence a graduated approach\nto opening the economy should be followed. Important civic activities like\nelections can be held while still imposing physical distancing. Sri Lanka’s\neconomic rekindling is linked to domestic needs as well as those of  its foreign trading  partners. <\/p>\n\n\n\n

The Covid-19\nepidemic has created a situation where working online is becoming\npermanently  institutionalized, and this\nis environmentally very desirable  in\nreducing travel stress, particulate dust and combustion of fossil fuels. The\nre-opening  should  make all such desirable features a permanent\ncharacteristic of the economy.<\/p>\n","protected":false},"excerpt":{"rendered":"

By Chandre Dharmawardana [This is a shortened version of a more technical paper, 15-04-2020] Introduction. An outbreak of a new type of  pneumonia like disease was first reported on 31st December 2019 from Wuhan City in the Hubei Province of China. It was identifies as caused by  a ‘Novel Corona Virus’ on 7th January 2020, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":true,"template":"","format":"standard","meta":{"footnotes":""},"categories":[85],"tags":[],"class_list":["post-101219","post","type-post","status-publish","format-standard","hentry","category-chandre-dharmawardana"],"_links":{"self":[{"href":"https:\/\/www.lankaweb.com\/news\/items\/wp-json\/wp\/v2\/posts\/101219","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.lankaweb.com\/news\/items\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.lankaweb.com\/news\/items\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.lankaweb.com\/news\/items\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.lankaweb.com\/news\/items\/wp-json\/wp\/v2\/comments?post=101219"}],"version-history":[{"count":0,"href":"https:\/\/www.lankaweb.com\/news\/items\/wp-json\/wp\/v2\/posts\/101219\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.lankaweb.com\/news\/items\/wp-json\/wp\/v2\/media?parent=101219"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.lankaweb.com\/news\/items\/wp-json\/wp\/v2\/categories?post=101219"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.lankaweb.com\/news\/items\/wp-json\/wp\/v2\/tags?post=101219"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}