Evidence for lack of transmission by close contact and surface touch in a restaurant outbreak of COVID-19

Abstract

Background: Coronavirus disease 2019 (COVID-19) is primarily a respiratory disease that has become a global pandemic. Close contact plays an important role in infection spread, while fomite may also be a possible transmission route. Research during the COVID-19 pandemic has identified long-range airborne transmission as one of the important transmission routes although lack solid evidence.

Methods: We examined video data related to a restaurant associated COVID-19 outbreak in Guangzhou. We observed more than 40,000 surface touches and 13,000 episodes of close contacts in the restaurant during the entire lunch duration. These data allowed us to analyse infection risk via both the fomite and close contact routes.

Results: There is no significant correlation between the infection risk via both fomite and close contact routes among those who were not family members of the index case. We can thus rule out virus transmission via fomite contact and interpersonal close contact routes in the Guangzhou restaurant outbreak. The absence of a fomite route agrees with the COVID-19 literature.

Conclusions: These results provide indirect evidence for the long-range airborne route dominating SARS-CoV-2 transmission in the restaurant. We note that the restaurant was poorly ventilated, allowing for increasing airborne SARS-CoV-2 concentration.

Keywords: Airborne; Close contact; Covid-19; Fomite; Human behavior.

Fig. 1

Diner positions and arrangement of the restaurant. (A) Floor plan sketch; (B) The 3D views of the three cameras.

Fig. 2

Characteristics of surface touch classified by sub-surfaces: (A) touch frequency; (B) number of people who touched the surface. (Touch frequency (${\delta }_{\mathrm{A}}$) and average number of people ($\overline{P_A})$ who touched the sub-surface A is calculated by considering only the individual who had touched A: ${\delta }_{\mathrm{A}}=\frac{{\sum }_{i=1}^{P_A}{N}_A\left(i\right)}{{\sum }_{i=1}^{P_A}{t}_A\left(i\right)}$, where $P_A$ is the total number of people who had touched A during the statistical period, $N_A\left(i\right)$ is the total number of touches on A by individual i, $t_A\left(i\right)$ is the total valid time of individual i staying in the restaurant; $\overline{P_A}=\frac{{\mathrm{P}}_{\mathrm{A}}}{S_A}$, where $S_A$ is the total number of A in the restaurant.).

Fig. 3

Surface touch network between (A) diners and personal surfaces (e.g. mucous, hand, body, and personal private objects) of diners; (B) staff and personal surfaces of staff; (C) individuals and private table objects; (D) individuals and public table objects; (E) individuals and public restaurant objects. (Circle, ellipse, and square show the individual, table, and public restaurant objects, respectively. Blue lines show that diners touched individual surfaces of diners sitting in the same table; red lines show diners touched individual surfaces of diners from other tables or touched the public table surfaces of other tables; blue numbers in (E) show the ID of public restaurant objects, which are shown in Fig. S4 and Table S2.

Fig. 4

Probability distribution of duration per contact. (A) Close and long contacts; (B) between diner-diner, diner-staff, and staff-staff.

Fig. 5

Close contact matrices of number of contacts (left-upper triangle) and total duration of contacts (right-bottom triangle) between two individuals. (ID of diners increases from bottom to top and from left to right on y and x axes, respectively. T01 to T18 are tables).

Fig. 6

Virus absorption from mucous surface via fomite route under different combinations of possible index case (IP) (Fig. S3): the inside elevator button was touched by the index patient. (Red, yellow, black, and blue bars indicate possible index patient, secondary infected diner, non-infected diner, and staff, respectively).

Fig. 7

Aerosol intake (ml) via close contact routes for different combinations of index patients (IP) (Fig. S3). (Red, yellow, black, and blue bars show the index patient, secondary infected cases, and susceptible diners, and susceptible staff. Only D1 to D10 were shown because there was no close contact between diners in T01 and diners at other tables.).