The outbreak of COVID-19 has affected the world with over two million cases globally. Malaysia has witnessed over 5,000 with almost 100 deaths as of 22 April 2020. Knowledge on the incubation period of COVID-19 is scarce due to the novelty of the virus. The aim of this study was to determine the incubation period of COVID-19 infection in the district of Petaling in Malaysia. A cross-sectional study was conducted using secondary data from the Petaling District Health Office. We analysed data of laboratory-confirmed COVID-19 cases notified to the Petaling District Health Office between 3 February 2020 and 13 April 2020. Our study included 219 cases. The median incubation period of COVID-19 among the cases was five days (interquartile range 3.0-8.0). Four main clusters were identified, with significant difference found between two of the clusters. Cluster A has a shorter incubation period 3.5 (3.0-6.8) compared to cluster B as most of the confirmed cases knew the source of infection. COVID-19 incubation period in Petaling, Malaysia fits within the range estimated by the World Health Organization. Based on the upper value of the incubation period interquartile range in our study, the length of quarantine and period of contact tracing should be at least 8 days. This finding is in accordance with our current practice to control the spread of COVID-19

Inntroduction: The rapid spread of the Coronavirus disease 2019 (COVID-19) worldwide has led the World Health Organization to declare COVID-19 outbreak as a pandemic on March 11, 2020. As the local studies on factors leading to the absence or presence of clinical illness among the COVID-19 cases are sparse, the study aims to determine the factors associated with asymptomatic COVID19 patients in Petaling District, Selangor, Malaysia Methods: Data on COVID-19 patients were extracted from the database of confirmed cases in Petaling District Health Office, Selangor, Malaysia from 3rd February 2020 to 30th April 2020. An asymptomatic laboratory-confirmed case is a person infected with COVID-19 who does not develop any symptoms. The study included socio-demographic variables, the detailed information on clinical manifestations and co-morbidity of the patients. Descriptive and multiple logistic regression analyses were conducted to determine the factors associated with asymptomatic patients. Results: The overall COVID-19 patients in Petaling District were 434. Approximately 70% (n= 292) of the patients were symptomatic while 32.7% (n= 142) were asymptomatic. Multivple logistic regression analyses revealed that factors significantly associated with asymptomatic patients were age below 40 years old (aOR: 1.79, 95% CI 1.11, 2.86), non-Malaysians (aOR: 3.22, 95% CI 1.44, 7.19) and local cases (aOR: 2.51, 95% CI 1.42, 4.42). Gender, ethnicity, comorbidity and township were not significantly associated with asymptomatic patients. Conlcusion Approximately one-third of COVID-19 patients were asymptomatic and the risk factors identified were younger age, non-Malaysians and local cases. Rigorous epidemiological investigation is helpful in identifying COVID-19 cases among these group of people who are asymptomatic.