Rapid asymptomatic transmission of COVID-19 during the incubation period demonstrating strong infectivity in a cluster of youngsters aged 16-23 years outside Wuhan and characteristics of young patients with COVID-19: A prospective contact-tracing study

Abstract

Background: The outbreak of coronavirus-disease-2019 (COVID-19) has rapidly spread to many places outside Wuhan. Previous studies on COVID-19 mostly included older hospitalized-adults. Little information on infectivity among and characteristics of youngsters with COVID-19 is available.

Methods: A cluster of 22 close-contacts of a 22-year-old male (Patient-Index) including youngsters with laboratory-confirmed COVID-19 and hospitalized close-contacts testing negative for severe-acute-respiratory-syndrome-coronavirus-2 (SARS-CoV-2) in Anhui Province, China was prospectively-traced.

Results: Since January 23, 2020, we enrolled a cluster of eight youngsters with COVID-19 (median age [range], 22 [16-23] years; six males) originating from Patient-Index returning from Wuhan to Hefei on January 19. Patient-Index visited his 16-year-old female cousin in the evening on his return, and met 15 previous classmates in a get-together on January 21. He reported being totally asymptomatic and were described by all his contacts as healthy on January 19-21. His very first symptoms were itchy eyes and fever developed at noon and in the afternoon on January 22, respectively. Seven youngsters (his cousin and six classmates) became infected with COVID-19 after a-few-hour-contact with Patient-Index. None of the patients and contacts had visited Wuhan (except Patient-Index), or had any exposure to wet-markets, wild-animals, or medical-institutes within three months. For affected youngsters, the median incubation-period was 2 days (range, 1-4). The median serial-interval was 1 day (range, 0-4). Half or more of the eight COVID-19-infected youngsters had fever, cough, sputum production, nasal congestion, and fatigue on admission. All patients had mild conditions. Six patients developed pneumonia (all mild; one bilateral) on admission. As of February 20, four patients were discharged.

Conclusions: SARS-CoV-2-infection presented strong infectivity during the incubation-period with rapid transmission in this cluster of youngsters outside Wuhan. COVID-19 developed in these youngsters had fast onset and various nonspecific atypical manifestations, and were much milder than in older patients as previously reported.

Keywords: COVID-19; Characteristics; Cluster of youngsters; Incubation period; Infectivity; Outside Wuhan; Prospective contact-tracing study; Rapid transmission.

Fig. 1

Representative transverse chest computed tomography scan images. (A) Day 1 after illness onset for Patient Index. A few infiltrates (slight slice-like shadow with increased density) in the lower lobe of the right lung were seen. (B) Day 3 after illness onset for Patient Index. In the peripheral zones of both lungs, scattered ground-glass opacities with fuzzy edges were seen, suggesting bilateral pneumonia with highly likely viral nature. (C) Day 2 after illness onset for Patient 3. A few infiltrates and ground-glass opacities were detected in the lower lobe of left lung. (D) Day 3 after illness onset for Patient 4. Ground-glass opacities and infiltrates in the right lung were observed. (E) Day 2 after illness onset for Patient 7. Small patchy and mottling high-density sub-pleural shadows were seen in the upper lobe of left lung. (F) Day 5 after illness onset for Patient 7. The left upper lung lesion progressed. Antiviral therapy started. (G) Day 13 after illness onset for Patient 7. Patchy blurring infiltrates in the peripheral parts of the left lung with obscure boundary remained. (H) Day 21 after illness onset for Patient 7. The patchy ground-glass density shadows and infiltrates with fuzzy edges in the left lung had been obviously absorbed. (I) Day 3 after illness onset for Patient 8. Few strip-like shadows with uneven density were seen in both lungs. (J) Day 6 after illness onset for Patient 8. Multifocal ground-glass density shadows and opacities in the peripheral parts of both lungs were observed. Antiviral therapy started. (K) Day 14 after illness onset for Patient 8. The multiple patchy high-density shadows consistent with novel coronavirus pneumonia with unclear boundary seen in the peripheral parts of both lungs progressed. (K) Day 18 after illness onset for Patient 8. Absorption of pneumonia lesions in both lungs was observed compared to the previous scan.