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 Pre-publication manuscripts are preliminary reports and have not been peer-reviewed.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. The most common symptoms seen were fever (43.8%), cough (31.6%) and sore throat (16.2%). Total number of close contacts to confirmed COVID-19 cases were 7081. There were 51 (31.9%) confirmed COVID-19 cases among close contacts of asymptomatic index cases and 109 (68%) were symptomatic index cases.
A total of 294 cases (67.3%) did not have any co-morbids while 16% had hypertension and 10.6% had diabetes mellitus. 62.5% had a close contact with a confirmed COVID-19 case and 76.7% were local infections. In Petaling, there are four cluster of cases identified being from religious gatherings (20.4%), in a corporate company (15.1%), health facilities (10.3%) and wholesale wet market (6.4%). Others would include sporadic local and imported cases.
Table 1: Baseline Characteristics of Patients with COVID-19 in Petaling District
N %
Total number of COVID-19 cases
437
Attack Rate 0.024
Age (mean, sd) 41, 17.7
Age group
0-10 15 3.4
11-20 28 6.4
21-30 112 25.6
31-40 77 17.6
41-50 59 13.5
51-60 77 17.6
>60 69 15.8
Gender
Male 235 53.8
Female 202 46.2
Nationality
Malaysian 402 92.0
Non- Malaysian 35 8.0
Symptomatic status
Symptomatic 282 64.5
Asymptomatic 155 35.5
Symptoms
Fever 187 43.8
Cough 137 31.6
Sore throat 71 16.2
Headache 22 5.0 Loss of taste and
smell
21 4.8
Myalgia 18 4.1
GI disturbances 12 2.7
Co-morbid /Risk factors
No 294 67.3
Hypertension 70 16.0
Diabetes mellitus 46 10.6
Dyslipidemia 22 5.0
Heart disease 16 3.7
Bronchial asthma 10 2.3
History of close contact with a confirmed COVID-19 case
Yes 273 62.5
No 164 37.5
Total number of close contacts Symptomatic index cases
4568 64.5
Asymptomatic index cases
2513 35.5
Confirmed COVID-19 cases among close contacts Symptomatic index
cases
109 68.1
Asymptomatic index cases
51 31.9
Type of Infection
Local 335 76.7
Import 102 23.3
Clusters
Religious gathering
89 20.4
Corporate company
66 15.1
Health facilities 45 10.3
Wholesale wet market
28 6.4
Others 209 47.8
Local council area subdivision
Petaling Jaya 178 40.7
Subang Jaya 100 22.9
Shah Alam 157 36.0
Others 2 0.5
Status
Alive 427 97.7
Dead 10 2.3
DISCUSSION
This study reported the epidemiological characterization of recent novel coronavirus infection outbreak in the most densely populated district in Selangor state, Malaysia. Most of the reported cases were aged 21-30 years old (25.6%) and there was not much difference in term of gender distribution. The age characterization is consistent with the initial outbreak reported in China and it was also contributed by cases from the workplace cluster(13). About 65% of the cases were symptomatic with the three most common symptoms reported including fever, cough and sore throat. Severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) which causes COVID-19, has pathogenesis of causing both upper and lower respiratory tract infections(14). Characterization of the earliest outbreak in epicentre of Wuhan was also described to have respiratory tract infection symptoms among majority of reported cases (15). Respiratory viruses are highly contagious when a patients are symptomatic. In this reported outbreak, more than half of cases were locally transmitted infection and had close contact with a confirmed COVID- 19 case. As an emerging acute respiratory infection disease, COVID-19 primarily can be transmitted through respiratory droplets (6) and contact (16). Thus, evidence of human- to-human transmission among close contacts has occurred since the initial period of this pandemic in the middle of December 2019 (17). Furthermore, clusters of COVID-19 cases in Petaling district were involving people gathering that further enhance spreading of virus in community (18). In addition, this outbreak reported about 32% from COVID-19 infected close contacts were epidemiological linked to asymptomatic cases of COVID-19. Since there was a reported similarity of viral loads transmission between symptomatic and asymptomatic cases (15) , the possibility of SARS-COV-2 transmission by asymptomatic
cases is likely to occur in community. The salivary glands could act as potential reservoir for COVID-19, thus when an asymptomatic COVID-19 infector is speaking, sneezing or even breathing, infectious salivary droplets could be transmitted to a susceptible host via mouth, eyes or directly inhaled into lungs (19). Few outbreak reports also provided similar evidence of virus transmission from asymptomatic infector to close contacts (20) (21).
Considering the novelty of SARS-COV-2, evidence accumulation of virus transmission from asymptomatic infected person has contribute to disease dynamicity that give public health implications. The asymptomatic COVID-19 infected individual should be considered as a source of infection. Therefore, strict monitoring of close contacts to asymptomatic infected cases is essential to contain potential outbreak.
In this study, fundamental epidemiologically value of the COVID-19 epidemic curves in Petaling district in presented. From the epidemic curve of all clusters in Petaling district from January until June 2020 (as in figure 1), the outbreak was interpreted as having propagated source pattern of spreading. This trend is consistent with person-to-person spreading in the outbreak of this newly introduced zoonotic viral pathogen that subsequently become capable of human-to-human transmission due to high mutation and recombination rates (22) . As shown in epidemic curve, the outbreak that occurred in Petaling district has multiple surges of COVID-19 cases, resulted from several main clusters, corporate company, religious gathering, health facilities, wholesale wet market and other sporadic cases. The source of infection for the index case from corporate company cluster was believed to be imported from Indonesia during travelling prior to the onset of symptoms. Subsequently, while having symptoms of being infected, the index
case attended a meeting at office and further transmission of virus occurred among the other workers. As for religious gathering cluster, the event became a catalyst for subsequent spread of COVID-19 not only in Petaling district, also resulted in massive transmission of COVID-19 infection in Malaysia. The religious gathering was attended by more than 19 000 people from various countries and this single mass gathering resulted in further international spread (23). In this religious gathering, it involved the sharing of communal space such as prayer hall, collective eating from one plate and sharing of sleeping area which likely to increase transmission ability among the participants.
Transmissibility of COVID-19 in these two main reported clusters in Petaling district were beyond from household contacts where virus transmission was up to 5th generation of contacts. On the basis of this epidemic curve, cluster transmission accounts for more than half of COVID-19 confirmed cases where the similar phenomenon had been seen in some other cities (16).
The Chinese outbreak of COVID-19 was declared to be a Public Health Emergency of International Health Concern by World Health Organization (WHO) on 30th January 2020 following the international spread of disease that poses a risk to public health worldwide.
Malaysia’s preparedness and response plan began as early as December 2019, focusing on public health activities, intensification of diagnostic capacity and early appropriate treatment of confirmed COVID-19 case (24). Following notification of a confirmed COVID-19 case, DHO will implement the control and prevention action. Thorough epidemiological investigation will be conducted by DHO in order to identify source of infection or index case. In order to break the virus transmission, confirmed COVID-19
case will be isolated and treated in designated COVID-19 hospital while contact tracing activity take place by identification of close contacts for mandatory COVID-19 laboratory testing and followed by 14-days home isolation order. Early detection of case among close contacts of confirmed COVID-19 case is critically crucial for early containment to prevent further seeding of community transmission.
Figure 1: COVID-19 Epidemiology Curve of all Clusters in Petaling District from January to June 2020
The early implementation of Movement Control Order (MCO) in response to the COVID- 19 pandemic based on Prevention and Control of Infectious Diseases Act 1988 played a vital role in controlling the outbreak and preventing disease transmission within the
0 2 4 6 8 10 12 14 16 18 20
21.1.2020 26.1.2020 31.1.2020 5.2.2020 10.2.2020 15.2.2020 20.2.2020 25.2.2020 1.3.2020 6.3.2020 11.3.2020 16.3.2020 21.3.2020 26.3.2020 31.3.2020 5.4.2020 10.4.2020 15.4.2020 20.4.2020 25.4.2020 30.4.2020 5.5.2020 10.5.2020 15.5.2020 20.5.2020 25.5.2020 30.5.2020
Number of Cases
Date of Onset
Corporate company Religious Gatherings Health Facilities Wholesale Wet Market Others
community. Closure of all universities, schools, religious places, and non-essential sectors during MCO further accommodated the breakage of virus transmission in community setting by prohibition of mass movements and gathering nationwide. This federal response was successfully declining the epidemic curve of COVID-19 outbreak in the Petaling district (as figure 1). The Enhanced Movement Control Order (EMCO), which is a cordon sanitaire implemented by federal government had eased COVID-19 outbreak in Petaling district further during wholesale wet market cluster.
Overall, this study provides valuable findings regarding the entire outbreak of COVID-19 in the district of Petaling and general epidemiological measures taken to curb the outbreak. Besides that, a large number of cases were included in this study as Petaling is part of the state of Selangor which is the second largest contributor of confirmed COVID-19 cases in Malaysia during this pandemic. Nevertheless, this study did encounter some limitations such as lack of data regarding severity and clinical outcome of the cases. Data gathered were also retrospective and self-reported by patients, hence may be inaccurate due to recall bias.
CONCLUSION
This study elicited several key conclusions in Petaling COVID-19 outbreak consistent with other studies. Majority of cases had a history of close contact with confirmed COVID-19 cases confirming human-to-human transmission. This study also showed that asymptomatic cases are still able to transmit the disease to others and this key finding needs to be shared with the community to ensure continuous practice of wearing face
masks, hand hygiene and social distancing in public. Public health efforts should be focused on surveillance for cases acquired locally with swift control measures to avert widespread community transmission. Furthermore, active case detection and quarantine among close contacts of confirmed cases is a key prevention and control strategy to prevent spread of the disease, while strict monitoring of close contacts to asymptomatic infected cases is just as important as those with symptoms. Further research is needed to better understand the transmission of SARS-CoV-2 from asymptomatic cases.
REFERENCES
1. World Health Organization. Novel Coronavirus (2019-nCoV) Situtation Report 1.
2020.
2. World Health Organization (WHO). Coronavirus disease (COVID-19) Situation Report-209. 2020.
3. Ministry of Health Malaysia. KENYATAAN AKHBAR KEMENTERIAN KESIHATAN MALAYSIA. 2020 Mar 15;
4. Shah AUM, Safri SNA, Thevadas R, Noordin NK, Rahman AA, Sekawi Z, et al.
COVID-19 outbreak in Malaysia: Actions taken by the Malaysian government. Int J Infect Dis. 2020 Aug 1;97:108–16.
5. Prime Minister’s Office of Malaysia. Restriction of Movement Order [Internet].
PMO Official Website. 2020 [cited 2020 May 6]. Available from:
https://www.pmo.gov.my/2020/03/movement-control-order/
6. Rothan HA, Byrareddy SN. The epidemiology and pathogenesis of coronavirus disease (COVID-19) outbreak. J Autoimmun. 2020;109(February):102433.
7. Huang C, Wang Y, Li X, Ren L, Zhao J, Hu Y, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet [Internet]. 2020 Feb 15 [cited 2020 Aug 27];395(10223):497–506. Available from:
https://isaric.tghn.org/protocols/
8. World Health Organization (WHO). Coronavirus disease (COVID-19) Situation Report-73 [Internet]. 2020 [cited 2020 Aug 27]. Available from:
https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on- covid-19-final-
9. Zurairi AR. Health DG: Petaling Jaya, Lembah Pantai lead Covid-19 cases. Malay Mail [Internet]. 2020 Mar 22 [cited 2020 May 6]; Available from:
https://www.malaymail.com/news/malaysia/2020/03/22/health-d-g-petaling-jaya- lembah-pantai-lead-covid-19-cases/1848902
10. Minitry of Health Malaysia. Panduan Notifikasi Penyakit Berjangkit CDIS (eNotifikasi). 2018.
11. Constitution of Malaysia. Prevention and Control of Infectious Diseases Act 1988.
2006.
12. Department of Statistics Malaysia. Population Distribution and Basic Demographic Characteristics 2010. Dept of Statistics, Malaysia. 2011. p. 1–133.
13. Prevention CC for DC and. The epidemiological characteristics of an outbreak of 2019 novel coronavirus diseases (COVID-19) in China. Vol. 2, CCDC Weekly.
2020.
14. Chen J. Pathogenicity and transmissibility of 2019-nCoV—A quick overview and comparison with other emerging viruses. Microbes Infect. 2020;22(2):69–71.
15. Lai CC, Shih TP, Ko WC, Tang HJ, Hsueh PR. Severe acute respiratory
syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease-2019 (COVID- 19): The epidemic and the challenges. Int J Antimicrob Agents.
2020;55(3):105924.
16. Han Y, Yang H. The transmission and diagnosis of 2019 novel coronavirus infection disease (COVID-19): A Chinese perspective. J Med Virol.
2020;92(6):639–44.
17. Tong Y, Ph D, Ren R, Med M, Leung KSM, Ph D, et al. Early transmission dynamics in Wuhan, China, of novel coronavirus- infected pneumonia. N Engl J Med. 2020;382(13):1199–207.
18. Rocklöv J, Sjödin H. High population densities catalyse the spread of COVID-19.
J Travel Med. 2020;27(3):1–2.
19. Fini MB. Oral saliva and COVID-19. Oral Oncol. 2020;108(104821).
20. Hu Z, Song C, Xu C, Jin G, Chen Y, Xu X, et al. Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China. Sci China Life Sci. 2020;
21. Mizumoto K, Kagaya K, Zarebski A, Chowell G. Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020. Eurosurveillance. 2020;25(10):1–
5.
22. Wang C, Horby PW, Hayden FG, Gao GF. A novel coronavirus outbreak of global health concern. Lancet. 2020;395(10223):470–3.
23. Fazila N, Mat C, Edinur HA, Khairul M, Abdul A, Safuan S. A single mass
gathering resulted in massive transmission of COVID-19 infections in Malaysia with further international spread. J Travel Med. 2020;19(April):1–4.
24. The Malaysian Response to COVID-19: Building Preparedness for ‘Surge Capacity’, Testing Efficiency, and Containment – From the Desk of the Director- General of Health Malaysia. kpkesihatan.
