08 June 2020
Lockdown and the law of unintended consequences: the impact of COVID-19 on waterborne infections within healthcare premises
Blog by Mike Weinbren.
Dr Weinbren is a Consultant Microbiologist and Infection Control doctor working at King’s Mill Hospital, Nottinghamshire.

Merton’s law, the law of unintended consequences, is a powerful force in nature. The law states that the actions of people, and especially of governments, always have effects that are unanticipated or ‘unintended’. Whether intended or not, viral infections of the respiratory tract often predispose to secondary bacterial infections through blockage of drainage of the upper respiratory tract due to inflammation or destruction of the muco-ciliary escalator. The unprecedented community lockdown and reduction in services within the hospital has meant that many water systems will have remained static or had reduced water turnover. These are ideal conditions for biofilm formation, which will now be accelerated by the warmer summer temperatures. The perversity of Merton’s law is that the well-intended and necessary lockdown measures to control SARS-CoV-2 may lead to ‘secondary’ bacterial infections with Legionella.

The ESGLI-ESCMID specialist group on Legionella infection, chaired by Susanne Surman-Lee, have been extremely proactive in producing a series of freely available guidelines on how to ensure your building water system is safe during and post COVID-19. The guidance covers dental water systems, nursing and care homes, hospital water systems and building water systems. Whilst prevention of Legionella is key, where infection does occur diagnostics are important not only for managing the individual patient but from a public health perspective in removing potential sources. Data from China suggests patients with COVID-19 may be more susceptible to a range of infections including Legionella, necessitating testing to exclude dual infection.1

COVID-19 may have had a wider impact on waterborne infections within healthcare premises. For example, in order to produce extra capacity for ventilatory care operating theatres were turned into ITUs overnight. Under all the pressures to prepare the hospital for this novel pandemic how many remembered to check the theatre water quality from a Pseudomonas perspective?

Coronaviruses can be detected in faeces. Amoy Gardens in Hong Kong became infamous during the SARS outbreak in 2003 because of the vertical transmission of this virus in a multi-storey apartment block. Residents on the same floor as the index case were not infected. Cases occurred in apartments connected by the same sewage system running vertically within the building. One explanation for the pattern of cases was the bathroom floor was connected to the main sewage pipe via a siphon (U bend) as the floors were meant to be wet mopped. Because this method of cleaning was not used the siphon was dry, and it was postulated that when the index case flushed the toilet an aerosol of faecal material containing virus was forced into the bathrooms thereby infecting individuals. Experimental work by Gormley et al. using Pseudomonas putida in a test rig has confirmed organisms can be disseminated across the drainage system by air movement, even moving up floors.2 When a toilet is flushed a bolus of faecal material and water enters the main sewer. As this falls, escaping trapped air is displaced upwards creating a faecal aerosol which is forced along the drainage system. In unoccupied areas of a building evaporation of water in U bends leads to loss of the seal providing a site for these aerosols to escape. Thus, low water turnover could lead to transmission of SARS-CoV-2 via this route.3

Whilst coronaviruses provided insight into the dynamics of sewers, sewage can provide insight into outbreak dynamics. Peccia et al. looked at SARS-CoV-2 RNA concentrations in primary sewage sludge in a north-eastern U.S. metropolitan area.4 Virus RNA concentrations were highly correlated with the COVID-19 epidemiological curve and hospital admissions. SARS-CoV-2 sewage RNA concentrations were a seven day leading indicator ahead of compiled COVID-19 testing data and led local hospital admissions data by three days.


  1. Xing Q, Li G, Xing Y, Chen T et al. (2020) Precautions are needed for COVID-19 patients with coinfection of common respiratory pathogens. medRxiv 20027698.
  2. Gormley M, Aspray TJ, Kelly DA, Rodriguez-Gil C (2019) Pathogen cross-transmission via building sanitary plumbing systems in a full scale pilot test-rig. PLOS One 12: e0171556.
  3. Gormley M, Aspray T, Kelly D (2020) COVID-19: mitigating transmission via wastewater plumbing systems. The Lancet https://doi.org/10.1016/S2214-109X(20)30112-1
  4. Peccia J, Zulli A, Brackney D, Grubaugh N et al. (2020) SARS-CoV-2 RNA concentrations in primary municipal sewage sludge as a leading indicator of COVID-19 outbreak dynamics. medRxiv 20105999.