Descriptive Epidemiology of the COVID-19 Pandemic in Petaling District
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This is an online COVID-19 pre-publication manuscript which has been submitted to WPSAR. Pre-publication manuscripts are preliminary reports and have not been peer-reviewed. They should not be regarded as conclusive, guide clinical practice/health-related behavior, or be reported in news media as established information. Descriptive Epidemiology of the COVID-19 Pandemic in Petaling District – “Can asymptomatic cases transmit the disease?” ABSTRACT Background: COVID-19 was first detected in Malaysia on 25th January 2020 with Petaling district’s first local transmission on 8th February 2020 involving multiple clusters. This study analyses descriptively the epidemiology of COVID-19 outbreak in Petaling from the first case to the end. Methodology: All data on laboratory confirmed COVID-19 cases in Petaling District Health Office from 1st February till 26th June 2020 were used. Socio-demographic characteristics, symptoms, date of onset, date of exposure, travel history and movement including comorbid history were obtained via phone interview using two specific investigation form templates. Descriptive epidemiology analysis according to time, place and person was done. Results: There were 437 COVID-19 positive cases with an incidence rate of 24 per 100,000 population. Total of 10 (2.3%) cases deaths were recorded with 427 recovered cases. From 437 cases, 35.5% remained asymptomatic whereas 64.5% were symptomatic with common symptoms of fever (43.8%), cough (31.6%) and sore throat (16.2%). Meanwhile 67.3% had no co-morbid, 62.5% reported history of close contact with a confirmed case and 76.7% were local infections. The transmission of the disease involved four main groups which were religious gatherings (20.4%), a corporate company (15.1%), health facilities (10.3%) and a wholesale wet market (6.4%). In 31.9% of confirmed cases, epidemiological link to asymptomatic index was observed. Conclusion: Asymptomatic cases are able to transmit the disease to others and this key finding needs to be shared to ensure continuous practice of wearing face masks, hand hygiene and social distancing in public. Further research is needed to better understand the transmission of SARS-CoV-2 from asymptomatic cases. Keywords: COVID-19, Asymptomatic COVID-19, Cluster COVID-19 INTRODUCTION The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or coronavirus disease (COVID-19) was first reported on 31st December 2019 in Wuhan, China (1). Since then, the virus has spread globally and affected more than 21 million people with more than 700 thousand deaths in less than a year(2). The presence of COVID-19 in Malaysia was first detected on the 25th January 2020 in three infected foreign travelers from China (3). Following that, the first Malaysian citizen was confirmed as the ninth case in early February 2020 (3). Localized clusters started to emerge in March with the largest cluster linked to a religious group gathering in Sri Petaling resulting in major increase in local cases and contributing to imported cases in neighboring countries (3). By 16th March, every state and federal territory in Malaysia has reported cases of COVID-19. Malaysia implemented the Movement Control Order (MCO) on 18th of March 2020 as a strategy to contain the spread of virus(4). The government initiative included closing international borders, shutting down certain economic sectors and a restriction on social movement within and between states to protect the population (5). Based on a large number of confirmed cases with exposure to the wet market in Wuhan, the SARS-CoV-2 pathogen was indicated to be zoonotic in origin. Reports have confirmed person-to person transmission via respiratory droplets as spread of virus occurred with persons in close contact with positive cases without exposure to living animals in Wuhan(6). The incubation period for COVID-19 is on average 5 days and can go up to 14 days with common reported symptoms of fever, cough, shortness of breath, fatigue and other flu-like symptom(7,8). There has also been incidence of asymptomatic cases documented. Petaling’s first COVID-19 was documented on 3rd February 2020 after a notification of a positive case was received. It was later confirmed that this imported case was also the first Malaysian to test positive for COVID-19(4). Subsequently, the number of cases in Petaling recorded a jump due to a localized cluster of COVID-19 infections from one corporate company with more than 90 cases confirmed within three weeks(9). The outbreak cases increased exponentially after that, triggering a more serious control response from the Petaling district health office. Resultant analysis of the COVID-19 cases in Petaling may provide critical information to help control future spread of similar infectious diseases within or external to the district and the whole country. Thus, the objective of this paper is to analyze and describe the epidemiology of COVID-19 epidemic in Petaling district. METHODS Study design This study is a descriptive study with exploratory analysis of all cases of COVID-19 notified to the Petaling District Health Office (DHO) from the beginning of the outbreak early February 2020 till end of June 2020. Study setting This study was conducted in the district of Petaling, a district located in the state of Selangor, Malaysia. The outbreak of COVID-19 in Petaling occurred in a highly urbanized area with a dense population. Case Definition The case definition for confirmed cases of COVID-19 in Petaling district is a person with laboratory confirmation using reverse transcriptase polymerase chain reaction (RT-PCR) method for COVID-19. Only cases that fit this case definition were included in this study. Epidemiological Investigation Each notified case is verified by the Petaling DHO before proceeding with an epidemiological investigation to determine the source of infection, contact tracing, active case detection and implementing prevention and control measures including quarantine orders. Case investigation and active case detection via contact tracing were carried out as part of the epidemiological investigation. The primary objective of investigation is to identify the source of infection and identify close contacts to the confirmed cases of COVID-19. Information on socio-demographic characteristics, illness symptoms and date of onset for COVID-19, date of exposure, travel history and movement including comorbid history were obtained via phone interview with cases and contacts using investigation form templates labelled as COVID-19/SEL SEV/1.2020 and COVID-19/SEL SEV/2.2020 form. The data from COVID-19/SEL SEV/1.2020 was then transferred into a Google Form and shared with the Selangor State Health Department making it easily accessible. Date of exposure was defined as the last date of contact with a known case of COVID-19 or last date of travel, if any, while date of onset was defined as the date the person self- reportedly develop any symptoms related to COVID-19. Meanwhile, details of close contacts were retrieved during case investigations a line listing of close contacts was created in Microsoft Excel format and sent to contact tracing team for further action. Daily monitoring of all cases and contacts were done throughout the following 14 days. All relevant data were captured within the COVID-19 surveillance system of Malaysia’s MOH. Data Management Majority of notification of confirmed cases of COVID-19 were received from the Surveillance Unit of the Selangor State Health Department. Some notifications were also received via phone calls, fax or email from hospitals and accredited laboratories. All notifications received were then added to a line listing in Microsoft Excel format. During the initial phase of the pandemic, COVID-19 was not included in the Ministry of Health (MOH) Malaysia has a surveillance system for notification and monitoring of infectious diseases known as Communication Diseases Control Information System (CDCIS) or eNotifikasi (10). COVID-19 surveillance was added to this surveillance system end of March 2020 in which person under investigation (PUI) and confirmed case of COVID-19 was made a mandatory notifiable disease to the nearest DHO. This is made compulsory under the Malaysia Prevention and Control of Infectious Disease Act 1988(11). All case records contained national identification numbers, and therefore all cases are recorded in the system without duplication. Data of all confirmed COVID-19 cases notified to the Petaling DHO from 1st February 2020 till 26th June 2020 were included in this study with universal sampling of all cases that fit the inclusion criteria. Data Analysis The socio-demographic and clinical characteristics of all confirmed cases of COVID-19 were summarized using descriptive statistics. Meanwhile, epidemic curve for all cases was constructed by plotting the number of cases (y-axis) versus self-reported date of symptom onset (x-axis). For asymptomatic cases, the last date of exposure was referred to as their date of onset. RESULTS There were 437 confirmed cases of COVID-19 in Petaling district where the first case was notified on 3rd February 2020 till the last notification on the 7th June 2020. The total population in Petaling district is 1,812,633 as reported by the Malaysian Census 2010(12). The incidence rate for COVID-19 infection is 24 per 100,000 population. The baseline characteristics of the confirmed cases are presented in Table 1 below. All 437 cases were admitted to the hospital for isolation and treatment. 427 cases recovered well, whereas 10 cases (2.3%) died due to further complications. 76.7% were local cases and 23.3% were imported cases. The mean age was 41 years old and 25.6% falls in the age group of 21-30 years old. Both genders were equally susceptible where males were 53.8% and females were 46.2%. 92% were reported to be Malaysian and 64.5% were symptomatic.