COVID-19: Outbreak Investigation Report

Abstract

Objective:
Various public health and social measures have been used during the COVID-19 outbreak, including lockdowns, contact-tracing, isolation and quarantine. The objective of this manuscript is to describe outbreaks of COVID-19 in Selangor, Malaysia, the public health strategies used and the observed impact of the measures on the epidemic curve.

Methods:
Information on all confirmed COVID-19 cases in Selangor between 25 January and 28 April 2020 was obtained. Clusters were identified, and cases were disaggregated into linked, unlinked and imported cases. Epidemic curves were constructed, and the timing of movement control orders was compared with the numbers of cases reported.

Results:
During the study period, 1395 confirmed COVID-19 cases were reported to the Selangor Health Department, of which 15.8% were imported, 79.5% were linked and 4.7% were unlinked cases. For two main clusters, the number of cases decreased after control measures were instituted, by contact-tracing followed by isolation and home quarantine for the first cluster (n = 126), and with the addition of the movement control order for the second, much larger cluster (n = 559).

Discussion:
The findings suggest that appropriate, timely public health interventions and movement control measures have a synergistic effect on controlling COVID-19 outbreaks.

Full text

https://ojs.wpro.who.int/ 1
WPSAR Vol 12, No 2, 2021 | doi: 10.5365/wpsar.2020.11.3.008
COVID-19: Outbreak Investigation Report
Severe acute respiratory syndrome coronavirus 2
(SARS-CoV-2) was first identified in Malaysia on
25 January 2020; three cases were notified, all
of which were imported from Wuhan, China. On 30
January 2020, WHO declared coronavirus disease 2019
(COVID-19) a public health emergency of international
concern. On 6 February, the first local transmission was
reported in Malaysia in a close contact of a confirmed
COVID-19 case who had returned from Singapore. The
first case in Malaysia with neither a history of contact
with a confirmed case nor travel to an affected area
was reported on 12 March 2020. By 28 April 2020,
Malaysia had reported 5851 confirmed cases and 100
fatalities.
Selangor is the most densely populated state
in Malaysia, with a population of 5.8 million and a
population density of 780.3 people/km2. It is situated
in Peninsular Malaysia, bordering the capital, Kuala
Lumpur, and the Federal Government Administrative
Centre, Putrajaya. By mid-March 2020, there were more
than 200 COVID-19 cases in Selangor, and the number
increased to more than 1300 by mid-April 2020, largely
due to two main clusters. The Malaysian Government
instituted movement restrictions through a mandatory
movement control order (MCO) under the Prevention
and Control of Infectious Diseases Act 1988 and the
Police Act 1967 to limit human movement from 18
March in an effort to prevent further COVID-19 cases.
A variety of containment strategies, used either
in isolation or in combination, have been used for
COVID-19, which can be broadly categorized as
physical distancing measures, movement restrictions,
public health measures and socioeconomic measures.1
This paper describes the epidemiology and control
measures used to control the outbreak of COVID-19 in
Selangor, Malaysia, up to April 2020.
a Ministry of Health Malaysia.
b Selangor State Health Department, Malaysia.
c Institute for Medical Research, Malaysia.
d Petaling District Health Ofce, Malaysia.
Published: 22 June 2021
doi: 10.5365/wpsar.2020.11.3.008
Objective: Various public health and social measures have been used during the COVID-19 outbreak, including lockdowns,
contact-tracing, isolation and quarantine. The objective of this manuscript is to describe outbreaks of COVID-19 in
Selangor, Malaysia, the public health strategies used and the observed impact of the measures on the epidemic curve.
Methods: Information on all confirmed COVID-19 cases in Selangor between 25 January and 28 April 2020 was obtained.
Clusters were identified, and cases were disaggregated into linked, unlinked and imported cases. Epidemic curves were
constructed, and the timing of movement control orders was compared with the numbers of cases reported.
Results: During the study period, 1395 confirmed COVID-19 cases were reported to the Selangor Health Department,
of which 15.8% were imported, 79.5% were linked and 4.7% were unlinked cases. For two main clusters, the number
of cases decreased after control measures were instituted, by contact-tracing followed by isolation and home quarantine
for the first cluster (n = 126), and with the addition of the movement control order for the second, much larger cluster
(n = 559).
Discussion: The findings suggest that appropriate, timely public health interventions and movement control measures
have a synergistic effect on controlling COVID-19 outbreaks.
Objective: Various public health and social measures have been used during the COVID-19 outbreak, including lockdowns,
contact-tracing, isolation and quarantine. The objective of this manuscript is to describe outbreaks of COVID-19 in
Selangor, Malaysia, the public health strategies used and the observed impact of the measures on the epidemic curve.
Methods: Information on all confirmed COVID-19 cases in Selangor between 25 January and 28 April 2020 was obtained.
Clusters were identified, and cases were disaggregated into linked, unlinked and imported cases. Epidemic curves were
constructed, and the timing of movement control orders was compared with the numbers of cases reported.
Results: During the study period, 1395 confirmed COVID-19 cases were reported to the Selangor Health Department,
of which 15.8% were imported, 79.5% were linked and 4.7% were unlinked cases. For two main clusters, the number
of cases decreased after control measures were instituted, by contact-tracing followed by isolation and home quarantine
for the first cluster (n = 126), and with the addition of the movement control order for the second, much larger cluster
(n = 559).
Discussion: The findings suggest that appropriate, timely public health interventions and movement control measures
have a synergistic effect on controlling COVID-19 outbreaks.
Use of movement restrictions during an
outbreak of COVID-19 in Selangor, Malaysia
Anita Suleiman,a Shaari Ngadiman,b Mazliza Ramly,a Ahmad Faudzi Yusoffc and Mohamed Paid Yusofd
Correspondence to Mazliza Ramly (drmazliza@moh.gov.my).

WPSAR Vol 12, No 2, 2021 | doi: 10.5365/wpsar.2020.11.3.008 https://ojs.wpro.who.int/
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Suleiman et alStrategies in stemming COVID-19 in Selangor, Malaysia
1 month to 92 years (median, 35 years); 10.4% were
aged <19 years, 46.5% 19–39 years, 27.2% 40–59
years and 14.5% ≥60 years. Of the 1395 cases, 15.8%
were imported, 79.5% were linked cases and 4.7% were
unlinked cases.
The epidemic curve (Fig. 1) shows an exponential
increase in the number of cases in Selangor from early
March 2020, which peaked on 19 March, followed by a
steady decline by 28 April.
Initial case detection and control measures included
contact-tracing, isolation of cases and home quarantining
of contacts of cases. Travellers and returning Malaysians
with either symptoms or fever detected with thermal
scanners at points of entry were tested for SARS-CoV-2.
Those found to be positive were isolated in a designated
COVID-19 hospital, while those found to be negative and/
or asymptomatic were quarantined in designated hotels
for 14 days from the date of arrival.
The increase in the number of linked cases after
22 February was due to a workplace cluster. Extensive
case investigations revealed 126 confirmed cases among
1715 contacts, for an attack rate of 7.3%. This attack
rate was higher among work-related contacts (18.7%,
56 of 300) than among family and social contacts
(4.9%). The case with the earliest onset of illness, on
18 February, was identified as the primary case for this
cluster and was imported from a neighbouring country.
The largest potential exposure event was on 27 February,
at a meeting with approximately 300 people. The number
of cases in this cluster peaked on 29 February and then
declined, in line with public health measures initiated on
29 February (Fig. 2A).
At the time of the workplace cluster, mass gather-
ings were not banned. A second cluster was subsequently
detected after a religious mass gathering in Kuala Lumpur
of more than 10 000 people between 28 February and
2 March 2020, resulting in 559 COVID-19 cases in
Selangor among attendees, their families and social con-
tacts (Fig. 2B). Further links were made to a wedding on
6 March and the transfer of students from a school near
the mass gathering location to another school in Selangor
on 12 March. The earliest onset of disease after the latter
event was on 26 February in a cook at the school in
Selangor, who also attended the mass gathering.
METHODS
This observational study included all COVID-19 cases
reported in Selangor between 25 January and 28 April
2020. By that time, Selangor had reported 25% of all
COVID-19 cases in Malaysia.
A confirmed case was defined as an individual with
a positive test for SARS-CoV-2 by reverse transcriptase-
polymerase chain reaction from nasopharyngeal swabs.
We obtained demographic, clinical and exposure
information from an online data collection form used by
district health authorities in case investigation. Clusters
were identified from detailed movement histories of
confirmed cases and their contacts.
An epidemic curve was plotted, with the date of
onset of illness used for symptomatic cases and the
date of last exposure plus 5 days as the estimated “on-
set date” for asymptomatic cases. We defined cases as
“imported” if they had travelled overseas in the 14 days
before onset, as “linked” if the disease was acquired
locally after a history of contact with a COVID-19 case
and as “unlinked” for those with no history of contact
with a confirmed COVID-19 case. Data were analysed in
Microsoft Excel with SPSS version 26.
The control measures used during the period of
measuring the epidemic curve are described.
Ethics approval
The study protocol was reviewed and approved by the
Medical Research and Ethics Committee, Ministry of
Health Malaysia (NMRR-20–1043–54912 [IIR]).
RE SULT S
As of 28 April 2020, 1395 confirmed COVID-19 cases
had been reported to Selangor Health Department. Most
(80%) were detected by contact-tracing, 13% were
imported, 5% were detected by sampling of people with
influenza-like illness or severe acute respiratory illness
at sentinel surveillance sites, and 2% were found during
routine passive case detection.
Most of the COVID-19 cases were in Malaysian
citizens (85%) and males (59%). The age range was

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Strategies in stemming COVID-19 in Selangor, MalaysiaSuleiman et al
During the first 14 days of the first MCO, the number
of COVID-19 cases decreased by 12.8%, with a further
decline of 71% after the second and 72% after the third
MCO. The number of imported cases fell after implemen-
tation of international travel restrictions during the first
MCO and had almost disappeared by the third. Most
unlinked cases were reported before and throughout the
first MCO and had also fallen to almost 0 during the third.
DISCUSSION
Lack of pharmacological treatment and vaccines against
COVID-19 meant that public health and social measures
were the mainstay of the initial COVID-19 response. Sel-
angor initially adopted contact-tracing, isolation of cases
and quarantine of contacts to manage the outbreak but
added MCOs with closure of schools, universities and
non-essential businesses and services. The MCOs ap-
pear to have flattened the epidemic curve. A modelling
study conducted in the United Kingdom that included
On 18 March, the first 14-day MCO was initiated,
which prohibited public movement, including interstate
and international travel and mass gatherings for religious,
sports, social and cultural activities throughout the
country. Businesses and services deemed non-essential,
schools, universities and government offices were closed,
and people were urged to work from home. Only essen-
tial services such as food and health care could operate,
with strict operating procedures that ensured physical
distancing and screening for fever. A second MCO was
implemented from 1 April to 14 April. In addition, an
enhanced MCO was enforced in certain locations with
established large clusters, where all movement was
restricted. Comprehensive testing of all residents for
SARS-CoV-2 was conducted; residents and visitors in the
area were forbidden to leave their homes, and all roads
into the enhanced MCO area were blocked. Residents
were provided with adequate food and medical supplies
by authorities, with special arrangements to address any
additional needs.
Fig. 1. Epidemic curve of COVID-19 cases by importation and linkage between 5 January and 28 April 2020,
Selangor, Malaysia (n = 1395)
MCO 1 MCO 2 MCO 3
0
10
20
30
40
50
60
70
1/5/20 1/19/20 2/2/20 2/16 /20 3/1/20 3/15/20 3/29/20 4/12 /2 0 4/26/20
Number of cases
Date of onset
Unlinked
Linked
Imported

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Suleiman et alStrategies in stemming COVID-19 in Selangor, Malaysia
Fig. 2A. Distribution of cases by date of illness onset and date of exposure in a workplace cluster, Selangor,
Malaysia (n = 126)
0
5
10
15
20
25
2/3/2 0
2/10/20
2/17/20
2/24/20
3/2/2 0
3/9/20
3/16/20
3/23/20
3/30/20
4/6/20
4/13/20
4/20/20
4/27/20
5/4/20
MCO
Date of onset Date of exposure
Fig. 2B. Distribution of cases by date of illness onset and date of exposure in a cluster in Selangor after attendance
at a mass religious gathering in Kuala Lumpur (n = 559)
0
10
20
30
40
50
60
70
80
90
2/11/2020
2/18/2020
2/25/2020
3/3/2020
3/10/2020
3/17/2020
3/24/2020
3/31/2020
4/7/2020
4/14/2020
4/21/2020
4/28/2020
Date of onset Date of exposure
MCO 1 MCO 2 MCO 3
Number of cases
Number of cases

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Strategies in stemming COVID-19 in Selangor, MalaysiaSuleiman et al
The objective of the MCO was to reduce contact
of potential cases with others, thereby averting wide-
spread community transmission and preventing the
health care system from being overwhelmed by an
influx of new patients. Extension of the MCO was made
possible by government support through an economic
stimulus package to ease the burden on businesses and
individuals of the economic downturn.8 Although costly,
MCOs were seen to slow the epidemic. An interrupted
time-series study in Hubei and Guangdong provinces in
China before and after lockdown showed a significant
reduction in the incidence of cases, indicating the ef-
fectiveness of lockdown in containing the outbreak.9 A
local modelling study with various contact rates during
the phases of MCO found that MCO implementation
flattened the epidemic curve,10 and the effectiveness
of lockdown in reducing transmission rates has been
shown by modelling elsewhere.2 It should be noted,
however, that the decrease in the number of COVID-19
cases in Selangor might have also been the effect of
the combined prevention strategies, such as isolation,
quarantine, travel bans and closure of schools and
universities, and not the MCO alone.
The study has several limitations. As Selangor
implemented several public health measures concur-
rently, the relative impact of each intervention could not
be evaluated. Nevertheless, our data show a temporal
association between trends in the epidemic curve and
MCO implementation. Additionally, we did not directly
assess changes in human contact behaviour before and
during the MCO.
Our study results support the conclusion that
MCOs, in conjunction with other public health and social
measures, played a key role in controlling the spread of
SARS-CoV-2 in Malaysia.
Acknowledgements
We thank the Director-General of Health Malaysia for
his permission to publish this article. We also extend our
gratitude to all personnel at the Selangor State Health
Department, district health offices and Sungai Buloh
Hospital and the Kuala Lumpur International Airport
Health Officer for their cooperation and work in collecting
the data for this study.
various transmission routes and mitigation measures
suggested that lockdowns alone, particularly if short,
will not eliminate transmission and that a combination
of stricter measures is required.2
One of the main public health measures used to
reduce importation of cases of COVID-19 was thermal
body scanning and health declarations at points of
entry. However, asymptomatic and presymptomatic
cases can effectively shed the virus3 and are unlikely to
be detected by screening at points of entry. One study
showed that half of infected travellers are not detected
during airport screening.4 In the initial workplace cluster
in Selangor, the index case was an imported case that
had not been detected at the point of entry. With a
substantial proportion of asymptomatic cases (30%),
additional control methods are required.
The initial workplace cluster in Selangor was suc-
cessfully interrupted through the public health measures
of contact-tracing, isolation of all confirmed cases and
home quarantine of all contacts. Contact-tracing has
been a key public health response during previous pan-
demics of influenza and other communicable disease
outbreaks, as it identifies potentially infected individu-
als before symptoms emerge.5 If conducted promptly,
contact-tracing can prevent onward transmission from
secondary cases.6 Although contact-tracing can be
highly effective for the control of COVID-19, it places
substantial demands on the public health authorities, as
reported in other studies.7
The second cluster, arising from the mass gathering
in Kuala Lumpur, involved cases all around the country
as attendees dispersed to their respective states. In
Selangor, contacting and then testing the large number
of potential contacts from this event stretched the
state’s capacity, and the response to the first cluster of
126 cases could not be replicated for the second cluster
of 559 cases. Therefore, the first MCO was enforced,
resulting in a reduction in the number of new cases,
which continued during the second and third MCOs.
Had mass gatherings been prohibited during the ear-
lier phase of COVID-19, this outbreak could have been
prevented. However, as a result of this cluster, MCOs
were identified as a useful, practicable control measure,
which can be implemented intermittently as required.

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Conicts of interest
We know of no conflict of interest associated with this
publication, and there has been no significant financial
support for this work that could have influenced its
outcome.
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