[COVID-19 One Month] From Incubation Period to Asymptomatic Infection... Issue Analysis

It has been a month since the first confirmed case of the novel coronavirus infection (COVID-19) in South Korea, marking 19 days since the initial diagnosis. After a Chinese woman (born in 1984) who arrived from Wuhan, China on the 20th of last month was confirmed positive and quarantined, a total of 31 infections have been reported in the country. Initially, confirmed cases were among those who had visited China, but secondary and tertiary cases emerged among family members and acquaintances who had close contact with these patients. As the number of confirmed cases increased, new instances of infection and outbreaks differing from previous cases appeared. Patients developed symptoms after the maximum known incubation period of 14 days, or were infected by individuals who showed no noticeable symptoms. Health authorities and clinical experts have focused on key COVID-19 issues such as the 'incubation period and asymptomatic infection.'

Patient develops symptoms 16 days after contact... Patient 28 and the incubation period mystery

Patient 28 (born in 1989, Chinese woman), who was confirmed positive on the 10th and discharged on the 17th, sparked controversy regarding the incubation period of this infectious disease. She is an acquaintance of Patient 3 (born in 1966, Korean man), who was confirmed positive on the 26th of last month. Both entered South Korea together from Wuhan on the 20th of last month. They visited a plastic surgery clinic in Gangnam, Seoul together on the 22nd and again on the 24th. At that time, Patient 3 was already experiencing symptoms such as fever and chills.

Patient 28 was confirmed positive 16 days after her last contact with Patient 3 on the 25th of last month. This exceeds the generally known maximum incubation period of 14 days for COVID-19. This raised questions about whether the quarantine period used by health authorities for epidemiological investigations should be extended. Previously, research from China suggested that the incubation period could be as long as 24 days.

The 28th domestic COVID-19 patient received isolation treatment at Myongji Hospital Regional Emergency Medical Center
[Photo by Yonhap News]

Regarding this, Jung Eun-kyeong, Director of the Korea Centers for Disease Control and Prevention (KCDC), stated, "(Patient 28) was receiving medical treatment unrelated to COVID-19 and was taking analgesics and antibiotics," adding, "Because she is young and continuously took analgesics, she may not have felt symptoms such as fever, muscle pain, or sore throat." She expressed a cautious stance. She further explained, "Analyzing the epidemiological characteristics of domestic patients shows that the most common incubation period is about 3 to 4 days, and even in longer cases, it is within 7 to 8 days," adding, "It is not appropriate to change the incubation period standard to over 14 days based on a single study."

Patient 28 underwent multiple diagnostic tests during isolation, showing ambiguous results alternating between negative and positive, leading to four tests before release from quarantine. Generally, COVID-19 patients are released from isolation if 48 hours have passed since symptoms disappeared and two consecutive real-time polymerase chain reaction (PCR) tests conducted 24 hours apart show negative results. On the 12th, her first test was inconclusive, showing borderline negative and positive results, but subsequent three tests were negative, leading to her release from isolation.

Gwak Jin, head of the epidemiological investigation and patient management team at the Central Disaster and Safety Countermeasures Headquarters, explained, "After review with the Central Clinical Task Force, it is believed that this patient was either asymptomatically infected or had mild symptoms in the early infection stage that were masked by the analgesics she was taking," adding, "When she was recently confirmed positive, clinical results indicated recovery, so this is not considered a case exceeding the incubation period."

Heightened attention on infection and transmission without symptoms... Controversy over quarantine rule violations

The three family patients numbered 25 to 27, who were confirmed positive on the 9th, attracted attention regarding 'asymptomatic infection.' None of them showed clear symptoms before their diagnosis. They only realized they were infected with the novel coronavirus after Patient 25 (born in 1946, Korean woman), the mother of Patient 26 (born in 1968, Korean man), was confirmed positive on the 8th. Patient 25 had symptoms such as fever, cough, and sore throat around the 6th and underwent virus testing at a clinic two days later, which confirmed her positive status. The next day, her son and daughter-in-law (born in 1982, Chinese woman) were urgently tested and both were confirmed positive. The couple had stayed in Guangdong Province, China from November last year to January 31 this year. After returning to Korea, the daughter-in-law had a mild persistent cough starting from the 4th but did not seek testing as symptoms were not severe. The son reportedly did not notice any symptoms.

Director Jung stated, "Since the daughter-in-law's cough started on the 4th, it is presumed she was the first to develop symptoms," and considered the possibility of asymptomatic infection to be low. However, the possibility that the mother was infected by her son, who showed no clear symptoms, cannot be ruled out. Clinical experts noted, "Even if patients have respiratory symptoms or fever, they may not recognize them or may continue daily activities during mild symptom phases, leading to 'mild infections,'" cautioning, "Mild infections where patients do not perceive illness but shed and transmit the virus should not be confused with asymptomatic infections." Health authorities and clinical experts also emphasized that the possibility of airborne transmission of COVID-19 is "low unless in limited environments such as respiratory procedures or mechanical ventilation in hospitals."

Medical staff are busy moving around for work at the screening clinic of the National Medical Center in Jung-gu, Seoul. Photo by Hyunmin Kim kimhyun81@

There was also a controversial case of a patient violating self-quarantine rules. Patient 15 (born in 1977, Korean man), who entered from Wuhan and was confirmed positive on the 2nd, had been under self-quarantine since the 29th of last month. However, on the 1st of this month, he dined with family members living on different floors of the same building. His sister-in-law was confirmed as Patient 20 (born in 1978, Korean woman) four days later.

According to related guidelines, individuals under self-quarantine must live alone in a separate space and eat alone. If unavoidable, they may communicate with family members but must maintain a distance of at least 1 meter while wearing masks and avoid face-to-face contact. Violating these guidelines can result in a fine of 3 million KRW under the Infectious Disease Prevention and Control Act. Health authorities confirmed, "Patient 15 did violate quarantine rules," and stated, "We will discuss with local governments whether to file charges." However, Patient 15 protested, saying, "I did not receive any guidelines on living rules from my family." The local government responsible for his residence explained, "We provided sufficient guidance on living rules via phone calls."