key: cord-1026942-42ghr9g4
authors: Amoruso, Irene; Baldovin, Tatjana
title: On-board toilets of long-haul flights: is sewage epidemiology effective for COVID-19 global surveillance?
date: 2021-02-26
journal: Travel Med Infect Dis
DOI: 10.1016/j.tmaid.2021.102006
sha: e332229f53033f5cb1bfc017e763625981f2acdd
doc_id: 1026942
cord_uid: 42ghr9g4

nan

We can think of COVID-19 as a Camusian plague, as emblematically stated by Sansonetti 1 in his interesting editorial that discusses the current coronavirus global emergency in terms of an "expected pandemic." In fact, COVID-19 is the third coronavirus epidemic in less than 20 years, following the outbreaks of SARS and MERS. In 2015, WHO coordinated an expert workshop on the prioritization of emerging pathogens. Prioritization criteria included the severity of the disease; the pathogen's potential to originate a public health emergency in the near future; and the absence of preventive and therapeutic countermeasures. Seven pathogens were identified as requiring urgent R&D and, consistently, highly pathogenic emerging coronaviruses relevant to humans were on the list. SARS and MERS indeed showed their rapid and disruptive effects as emerging pathogens. Besides the invaluable insights they provided on beta-coronaviruses' crossspecies transmission and their molecular pathogenesis mechanisms, their essential legacy was possibly that of recognizing the crucial importance of an orchestrated response in case of a rapidly disseminating global epidemic. However, despite major revisions of the International Health Regulations (IHR) and the many efforts made since then to improve surveillance networks, aspects of this coordination still leave much to be desired. Sensitive and flexible surveillance systems for early warning require further development.

The clinical detection of SARS-CoV-2 RNA in feces of infected people promptly lead to the idea of wastewater-based epidemiology (WBE) as a valuable strategy for COVID-19 environmental surveillance 3 . We have been personally working on COVID-19 WBE 4 , so the idea of translating the concept from urban wastewater to aircraft toilet waste (ATW) of long-haul flights (i.e. > 4,000 Km) came up quite naturally. Current evidence suggests that detection in community sewage of one symptomatic/asymptomatic infected case per 100 to 2,000,000 noninfected people is theoretically possible 5 . Even more so, this should be feasible when sampling J o u r n a l P r e -p r o o f the excreta collected by "dry" vacuum on-board toilets of long-haul flights, with a capacity of more than 200 passengers.

If we recall the case of SARS-CoV-2 and how it spread in Europe, we could probably say that it was a business class passenger. A comprehensive pre-COVID-19 review 6 Some details can be added to the hypothetical diagram of an ATW-based surveillance approach. Most likely, passengers allowed to board will either be not infected or asymptomatic/pauci-symptomatic/pre-symptomatic COVID-19 patients. Actually, recent J o u r n a l P r e -p r o o f publications support the presence and detectability of SARS-CoV-2 RNA in stools of such COVID-19 cases [9] [10] [11] . On a long-haul flight, they will probably avail themselves of the on-board toilet, thus enriching the content of the vacuum toilet septic tank. Of course, some passengers will not contribute to the common ATW sample but, intuitively, the rule is "the longer the flight, the greater the toilet usage and the representativeness of ATW". For long-haul routes, the general rule has toilet servicing being performed after landing of each individual flight. Minor exceptions could concern either airlines choosing to contract ground handling services under non-standard terms, or "empty leg" non-scheduled charter flights (i.e. aircraft flying with no passengers for repositioning). Nevertheless, such atypical situations can be identified a priori and their representativeness pondered. During servicing, a dedicated "honey truck" empties the aircraft septic tank(s), with the suction actually mixing the ATW quite thoroughly. An amount suitable for surveillance purposes (e.g. 0.5-1 L) could be sampled right from the truck or just before ATW is dumped in the disposal facility. The sample should then be processed as soon as possible. If SARS-CoV-2 RNA is detected, additional surveillance actions can be promptly extended to passengers. A passenger contact tracing protocol should be feasible thanks to the public health passenger-locator cards, as developed by the IHR.

Of course some practical aspects should be further scrutinized. For instance, we questioned the analytical suitability of ATW samples, due to the pre-filling of septic tanks with sanitation liquid during the ground toilet servicing. Although the precise composition (possibly nonylphenol ethoxylate or glutaraldehyde and benzalkonium chloride) of such liquids is not mentioned in ground operations manuals, toilet fluids are described as "corrosive" and could compromise the integrity of nucleic acids or other target biomolecules. Nevertheless, the above- In addition to technical aspects, we should also debate the near future of global travels. Unless a second massive COVID-19 wave occurs, air traffic will recover its pre-pandemic numbers in the coming months and years. In 2018, the global airline industry boarded more than 4 billion travelers, and this number was expected to double by 2037. The Asia-Pacific region is considered the biggest driver of demand in the airline industry. Before the COVID-19 pandemic,

China accounted for about 600 million passengers per year, and was set to conquer the world's largest aviation market before 2025, thus displacing the US. Besides Asia, the other fastestgrowing markets belong to Africa (e.g. Sierra Leone, Ivory Coast), so that by 2037 African countries will count 400 million passengers a year 12 .

With the COVID-19 pandemic, the world has once more been forced to acknowledge that emerging pathogens can escape from their cage and then rapidly spread worldwide. After all, it appears to be an unavoidable, if undesired, consequence of the contraction of geographic and social lengths in this era of globalization. Advanced molecular techniques for the detection of novel pathogens and the monitoring of known ones should constitute a stronghold for the global surveillance of infectious diseases. Furthermore, the 360-degree potential of ATW samples could also be exploited by investigating the multitude of targets (e.g. illicit drugs, pharmaceuticals, xenobiotics) already realized by classic WBE, thus going even beyond the sole surveillance of communicable diseases.

The time has come for a revolutionary approach to be implemented and it urgently needs the joint efforts of the international community. Pandemics can be restrained to a certain extent, J o u r n a l P r e -p r o o f 6 but ultimately the early identification of pathogens is our ace in the hole, together with the universality of science that should always prevail on politics, profits and fears.

COVID -19, chronicle of an expected pandemic

Progress in global surveillance and response capacity 10 years after severe acute respiratory syndrome

Potential Sensitivity of Wastewater Monitoring for SARS-CoV-2: Comparison with Norovirus Cases

SARS-CoV-2 RNA detection and persistence in wastewaters samples: an experimental network for COVID-19 environmental surveillance in Padua

Computational analysis of SARS-CoV-2/COVID-19 surveillance by wastewater-based epidemiology locally and globally: Feasibility, economy, opportunities and challenges

The Roles of Transportation and Transportation Hubs in the Propagation of Influenza and Coronaviruses: A Systematic Review -PubMed

Metagenomic analysis of viruses in toilet waste from long distance flights -A new procedure for global infectious disease surveillance

First confirmed detection of SARS-CoV-2 in untreated wastewater in Australia: A proof of concept for the wastewater surveillance of COVID-19 in the community

Asymptomatic SARS-CoV-2 infected case with viral detection positive in stool but negative in nasopharyngeal samples lasts for 42 days

Detection of SARS-CoV-2 in Fecal Samples From Patients With Asymptomatic and Mild COVID-19 in Korea

Detection of novel coronavirus by RT-PCR in stool specimen from asymptomatic child

IATA 20-Year Air Passenger Forecast. Press release: www

We wish to thank N.E. Baroni for disclosing and sharing a precious insight on these peculiar aspects of civil aviation. We also kindly thank Cat Anderson for her help with language editing.

None.

The authors declare no competing financial interest.J o u r n a l P r e -p r o o f