Suitability of aircraft wastewater for pathogen detection and public health surveillance

Abstract

International air travel is now widely recognised as one of the primary mechanisms responsible for the transnational movement and global spread of SARS-CoV-2. Monitoring the viral load and novel lineages within human-derived wastewater collected from aircraft and at air transport hubs has been proposed as an effective way to monitor the importation frequency of viral pathogens. The success of this approach, however, is highly dependent on the bathroom and defecation habits of air passengers during their journey. In this study of UK adults (n = 2103), we quantified the likelihood of defecation prior to departure, on the aircraft and upon arrival on both short- and long-haul flights. The results were then used to assess the likelihood of capturing the signal from infected individuals at UK travel hubs. To obtain a representative cross-section of the population, the survey was stratified by geographical region, gender, age, parenting status, and social class. We found that an individual's likelihood to defecate on short-haul flights (< 6 h in duration) was low (< 13 % of the total), but was higher on long-haul flights (< 36 %; > 6 h in duration). This behaviour pattern was higher among males and younger age groups. The maximum likelihood of defecation was prior to departure (< 39 %). Based on known SARS-CoV-2 faecal shedding rates (30-60 %) and an equal probability of infected individuals being on short- (71 % of inbound flights) and long-haul flights (29 %), we estimate that aircraft wastewater is likely to capture ca. 8-14 % of SARS-CoV-2 cases entering the UK. Monte Carlo simulations predicted that SARS-CoV-2 would be present in wastewater on 14 % of short-haul flights and 62 % of long-haul flights under current pandemic conditions. We conclude that aircraft wastewater alone is insufficient to effectively monitor all the transboundary entries of faecal-borne pathogens but can form part of a wider strategy for public heath surveillance at national borders.

Keywords: International air travel; Public health surveillance; SARS-CoV-2; Wastewater-based epidemiology.

Graphical abstract

Fig. 1

Evaluation of the likelihood that individuals would use the aircraft toilet to defecate on either a short-haul flight (A, B upper panels) or long-haul flights (C, D lower panels), stratified by either (A, C) gender, or (B, D) age. Sample size (short haul, n = 1872; long-haul n = 1620).

Fig. 2

Evaluation of the likelihood that individuals would use the airport terminal toilets to defecate either before boarding the plane (A, B upper panels) or upon landing in the UK (C, D lower panels), stratified by either (A, C) gender, or (B, D) age (n = 1909).

Fig. 3

Frequency distribution for the Monte Carlo simulation (n = 50,000) describing the probability of capturing individuals infected with SARS-CoV-2 through toilet use on either (A) short-haul, or (B) long-haul flights. LSL designates the lower boundary limit.

Fig. 4

Frequency distribution for the Monte Carlo simulation (n = 50,000) describing the number of infected individuals captured by wastewater on either international (A) short-haul or (B) long-haul flights. LSL denotes the lower boundary limit. Note the different x-axis and y-axis scales.