The outbreak of COVID-19: An overview


In late December 2019, a previous unidentified coronavirus, currently named as the 2019 novel coronavirus#, emerged from Wuhan, China, and resulted in a formidable outbreak in many cities in China and expanded globally, including Thailand, Republic of Korea, Japan, United States, Philippines, Viet Nam, and our country (as of 2/6/2020 at least 25 countries). The disease is officially named as Coronavirus Disease-2019 (COVID-19, by WHO on February 11, 2020). It is also named as Severe Pneumonia with Novel Pathogens on January 15, 2019 by the Taiwan CDC, the Ministry of Health and is a notifiable communicable disease of the fifth category. COVID-19 is a potential zoonotic disease with low to moderate (estimated 2%–5%) mortality rate. Person-to-person transmission may occur through droplet or contact transmission and if there is a lack of stringent infection control or if no proper personal protective equipment available, it may jeopardize the first-line healthcare workers. Currently, there is no definite treatment for COVID-19 although some drugs are under investigation. To promptly identify patients and prevent further spreading, physicians should be aware of the travel or contact history of the patient with compatible symptoms.



In late December 2019, an outbreak of a mysterious pneumonia characterized by fever, dry cough, and fatigue, and occasional gastrointestinal symptoms happened in a seafood wholesale wet market, the Huanan Seafood Wholesale Market, in Wuhan, Hubei, China.1 The initial outbreak was reported in the market in December 2019 and involved about 66% of the staff there. The market was shut down on January 1, 2020, after the announcement of an epidemiologic alert by the local health authority on December 31, 2019. However, in the following month (January) thousands of people in China, including many provinces (such as Hubei, Zhejiang, Guangdong, Henan, Hunan, etc.) and cities (Beijing and Shanghai) were attacked by the rampant spreading of the disease.2 Furthermore, the disease traveled to other countries, such as Thailand, Japan, Republic of Korea, Viet Nam, Germany, United States, and Singapore. The first case reported in our country was on January 21, 2019. As of February 6, 2020, a total of 28,276 confirmed cases with 565 deaths globally were documented by WHO, involving at least 25 countries.3 The pathogen of the outbreak was later identified as a novel beta-coronavirus, named 2019 novel coronavirus (2019-nCoV) and recalled to our mind the terrible memory of the severe acute respiratory syndrome (SARS-2003, caused by another beta-coronavirus) that occurred 17 years ago.

In 2003, a new coronavirus, the etiology of a mysterious pneumonia, also originated from southeast China, especially Guangdong province, and was named SARS coronavirus that fulfilled the Koch’s postulate.4 The mortality rate caused by the virus was around 10%–15%.5,6 Through the years, the medical facilities have been improved; nevertheless, no proper treatment or vaccine is available for the SARS.6 The emergence of another outbreak in 2012 of novel coronavirus in Middle East shared similar features with the outbreak in 2003.7 Both were caused by coronavirus but the intermediate host for MERS is thought to be the dromedary camel and the mortality can be up to 37%.5 The initial clinical manifestations for both SARS and MERS are usually nonspecific except that the majority of patients presented with fever and respiratory symptoms. Unprotected hospital staff who were exposed to patients’ droplets or through contact prone to be infected and nosocomial infections ensue.1,6 Furthermore, cases associated with travel had been identified for SARS, MERS, and COVID-19.5,8–11 Because of global transportation and the popularity of tourism, COVID-19 is a genuine threat to Taiwan.


Coronavirus is an enveloped, positive single-strand RNA virus. It belongs to the Orthocoronavirinae subfamily, as the name, with the characteristic “crown-like” spikes on their surfaces.5 Together with SARS-CoV, bat SARS-like CoV and others also fall into the genus beta-coronavirus. COVID-19 (caused by 2019-nCoV infection) is classified as a fifth-category notifiable communicable disease in Taiwan on January 15, 2019.12 The genus beta-coronavirus can be divided into several subgroups. The 2019-nCoV, SARS-CoV, and bat SARS-like CoV belong to Sarbecovirus, while the MERS-CoV to Merbecovirus.13 SARS-CoV, MERS-CoV, and 2019-nCoV all cause diseases in humans but each subgroup may have mild different biologic characteristic and virulence.5–7

The exact origin, location, and natural reservoir of the 2019-nCoV remain unclear, although it is believed that the virus is zoonotic and bats may be the culprits because of sequence identity to the bat-CoV.5,13 According to previous studies on the SARS- and MERS-CoV, epidemiologic investigations, their natural reservoir is bat, while palm civet or raccoon dog may be the intermediate (or susceptible) host for SARS-CoV and the dromedary camel for MERS-CoV.5,13 A field study for the SARS-CoV on palm civet ruled out the possibility as the natural reservoir (low positive rate); instead, the prevalence of bat coronavirus among wild life is high and it shares a certain sequence identity with the human SARS-CoV.14 Therefore, bats are considered the natural host reservoir of SARS-like coronavirus.13 However, the origin or natural host for the 2019-nCoV is not clear, although it might come from a kind of wild life in the wet market.1 Theoretically, if people contact or eat the reservoir or infected animal, they could be infected. However, to result in large scaled person-to-person transmission as in the past SARS outbreak, the virus must spread efficiently. Initially, the 2019-CoV outbreak was reported as limited person-to-person transmission and a contaminated source from infected or sick wild animals in the wet market may have been the common origin.1,2 But more and more evidences came out with clusters of outbreaks among family confirmed the possibility of person-to-person transmission.8,10,11,15,16 In addition, the involvement of human angiotensin-converting enzyme 2 (hACE2) as the cellular receptor (like SARS) made droplet transmission to the lower respiratory tract possible.5,17 Furthermore, contact transmission like SARS is also likely although the survival time in the environment for the 2019-nCoV is not clear at present. Currently, there was no evidence of air-borne transmission. Viral RNAs could be found in nasal discharge, sputum, and sometimes blood or feces.1,9,10,13,15 But whether oral-fecal transmission can happen has not yet been confirmed. Once people are infected by the 2019-nCoV, it is believed that, like SARS, there is no infectivity until the onset of symptoms.15 However, one report describes infection from an asymptomatic contact but the investigation was not solid.10 The infectious doses for 2019-nCoV is not clear, but a high viral load of up to 108 copies/mL in patient’s sputum has been reported.10 The viral load increases initially and still can be detected 12 days after onset of symptoms.9 Therefore, the infectivity of patients with 2019-nCoV may last for about 2 weeks. However, whether infectious viral particles from patients do exist at the later stage requires validation.


The illness onset of the first laboratory-confirmed case of 2019-nCoV infection was on December 1, 2019 in Wuhan, China (Table 1).1 Initially, an outbreak involving a local market, the Huanan Seafood Market, with at least 41 people was reported.1 The local health authority issued an “epidemiologic alert” on December 31, 2019, and the market was shut down on January 1, 2020. A total of 59 suspected cases with fever and dry cough were referred to a designated hospital (the Jin Yin-tan Hospital). Of the 59 suspected cases, 41 patients were confirmed by next-generation sequencing or real-time reverse transcription-polymerase chain reaction (RT-PCR). Twenty-seven (66%, 27/41) patients had history of Huanan Seafood Market exposure.1 However, there is a caveat that the first case on December 1 did not show history of Huanan Seafood Market exposure and the subsequent cases started on December 10, nine days later. In the following days, a burst of cases was spreading from Wuhan to the whole Hubei province. Subsequently, many cities and provinces were attacked by this virus. One of the reasons may be due to the heavy transportation load during the Chinese Lunar New Year (on January 25) period. The first exported case was into Thailand on January 13, 2020. However, the disease spread rapidly and globally. Not only familial clusters but also outbreaks in ocean liners were reported. As of February 6, 2020, a total of 28,276 confirmed cases with 565 deaths globally were documented by WHO, involving at least 25 countries.3 The WHO issued an public health emergencies of international concern (PHEIC) alarm on January 30, 2020. Many stringent quarantine procedures and fever surveillance were underway. The initial mortality rates for patients in the hospital were estimated to be 11%–15%,1,15 but more recent data were 2%–3%. It is very likely that person-to-person transmissions occur via droplets and contact. Nosocomial infections in the healthcare facilities did happen and stress the importance of good infection control.

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The outbreak of COVID-19: An overview - D'Olhos Hospital Dia