Epidemiology of Covid-19 Positive Patients Admitted In a Dedicated Covid Hospital

Introduction: The pandemic of Covid-19 was declared on 11 march 2020 by WHO. Methods: The study was carried out in a dedicated Covid 19 hospital on 1493 patients. All patients who tested positive for Covid-19 by RTPCR were included in the study and the outcome was analysed. Result: Most of the patients were symptomatic (64.97%). The asymptomatic patients recovered faster than symptomatic and the difference was statistically significant. The most common symptoms were fever (38.3%), tiredness (20.6%) and cough (17.8%). Only 0.8% patients died due to the novel corona virus. Conclusion: The mortality due to the virus in India is not alarming and we need to consider starting focusing back on other diseases as well. The mean age of the deceased was 58.42 which highlights that elderly at a greater risk to succumb to disease and hence should be preferred for as priority one for vaccination against the disease. The numbers of Covid-19 cases have reduced considerably over last few months in the country, but this does not mean that the pandemic has gone away. We need to be cautious, use this opportunity to vaccinate the maximum population to prevent second wave of the disease


INTRODUCTION
Corona viruses are large group of virus that infect both humans and animals.Novel Corona virus (Covid-19) started from China. 1 Covid-19 was declared pandemic by WHO on 11 march 2020. 2,3e complete epidemiology of the disease is not yet fully understood.Patients are the main source of infection.It is now clear that the virus is transmitted mainly through airborne route.Infection occurs when droplets generated during coughing, sneezing, talking or blowing nose are inhaled by other person in close contact.These droplets can land on the surfaces of the nearby objects.[6] Studies have found that the median incubation period is 5.1 days (Range 2-14 days). 1,7,8However few unusual cases of longer incubation period of 19 days have also been found. 9,10The 19-day incubation period is a low probability event, and experts suggest 14 days for quarantine.
The severity of COVID-19 was defined on the basis of the clinical features, laboratory testing, and chest radiograph imaging, including asymptomatic and symptomatic cases as mild, moderate, severe, or critical. 15][16] How far these preventive measure have been effective in controlling the spread of infection is a point of further discussion and research.
Identification, isolation and caring for patients early are essential to limit human-to-human transmission including reducing secondary infections among close contacts and health care workers, preventing transmission amplification events. 1 Beyond doubt it is certain that the best way to prevent the infection and end the pandemic of Covid-19 is by attaining herd immunity by immunisation. 14However percentage of population that needs to be vaccinated to attain herd immunity is not known and is a matter of research.Similarly other matters of research are, how long the immunity against virus will last after initial doses of vaccination?Which immunity is longer lasting that achieved through vaccination or natural infection is not known.In short a lot of questions about the epidemiology of the disease, its prevention and management are still in grey area and requires further research.
In present study we have tried to fill some gaps about the epidemiology of the Covid-19 infection.

METHODOLOGY
The study was conducted at Govt approved dedicated Covid-19 hospital in North-Bengal from Jun to Nov 2020.Patients were managed as per the guidelines issued from MoHFW. 17,18 is a prospective observational study.All the patients who were suspected to be Covid-19 were tested by RTPCR.All Covid-19 positive patients were then admitted in the study centre.Contact tracing of the positive patients was carried out, and all the high risk contacts were also tested by RTPCR.All patients who tested Covid-19 positive were included in the study.The RTPCR tests were done from ICMR approved lab.Consent from the participants was taken before including in the study.Approval from institutional ethics committee was taken.
The data was collected in a pre-structured questionnaire.Epidemiological determinants of these patients were studied.The data was analysed using SPSS software version 23.
Cured/recovered: Patient was considered cured or recovered when they tested negative by repeat RTPCR.

RESULTS
A total of 4890 patients were tested, out of which 1493 (30.53%) patients were found Covid-19 positive and treated during the study period.All the Covid-19 positive patients were included in the study.
Mean age of cases was 33.75 years with male preponderance (95.6%), similar to previous studies. 19,20st of the patients were symptomatic (64.97%), while only 34.23% patients were asymptomatic.The finding similar to previous studies 20,21 and in variance from study conducted in China.The difference in recovery time for symptomatic and asymptomatic cases was analyzed using chi square test and it was found that recovery time of asymptomatic patient was lower than that of symptomatic patient and there was significant difference between the two groups.(X 2 = 112.54,D.F=1 N=1481, p-value= <0.00001).These highlights that asymptomatic have shorter duration of viral shredding than sympto- matic and this could be due to better immunity of these patients against the virus.The finding is in variance with the study conducted in China. 22e most common symptom amongst the patients was Fever (38.3%) followed by tiredness (20.6%) and cough (17.8%).The presenting symptom of patients is shown in the table (multiple responses).

DISCUSSION
The daily new cases reached its peak of in early Aug 20 followed by a second peak in Oct 20.Till then the number of new cases per day have declined to near zero.The average no of new cases per day during the study period was 10.The occurrence of daily new cases/day graph is similar to national graph. 23,24The reduction of new cases/day has occurred in spite of the fact that there has been lifting of various bans national wide and increase in the no of testing centers.This reduction could be probably due to achievement of herd immunity amongst general population through natural infection.However larger studies to evaluate the attainment of herd immunity needs to be done.Also longitudinal studies to determine the period for which this immunity lasts needs to be done.Studies suggest the immunity after natural infection is short lived 25 , therefore we expected that sporadic outbreaks of the disease to occur off and on for years.Two vaccines against Covid-19 are now available in country, however how long the protection will be offered and how frequently booster doses will be required to achieve the herd immunity is not known.Attainment of herd immunity against the disease through vaccination is the best method to curb the pandemic.But percentage of vaccination coverage required to attain the herd immunity is to be researched.
There were 12 (0.8%) Covid-19 positive deaths during the study period which is similar to national data. 23,24However the death rate is much lower than other countries.2  Thicould be due to the fact that corona viruses are zoonotic, [29][30][31]

Figure 1 :Figure 2 :
Figure 1: Distribution of cases as per age 22

Table 2 : Most common symptoms amongst Covid- 19 positive patients (Original)
Asymptomatic cases of covid-19 are most common and they recover faster as compared to symptomatic ones.Fever, tiredness and cough are the most common symptoms.Death rate due to covid-19 in very low therefore we should need to focus back on others diseases which are still the maximum contributors of death in India.This is not trivializing Covid-19 but a message that in order to defeat Covid-19 others diseases should not get neglected and we should not deviate from the goal of improving the overall public health status of the country.The pandemic due to Covid-19 has now crossed its peak and the cases are declining.The downfall in number of cases is probably due to attainment of herd immunity through natural infection.This highlights that the actual number of Covid-19 cases in the country could have been much larger than what is reported.How long the immunity due to natural infection will last is not known, however going by the fact that immunity due to infection by other corona viruses is short lived we assume that sporadic outbreaks of the disease is highly possible.Mass vaccination to cover maximum people as early as possible is warranted to end the pandemic.High risk groups like people above 50 years, health care workers and front line workers should be given priority during vaccination.