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Reducing risks from coronavirus transmission in the home—the role of viral load

BMJ 2020; 369 doi: https://doi.org/10.1136/bmj.m1728 (Published 06 May 2020) Cite this as: BMJ 2020;369:m1728

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  1. Paul Little, professor1,
  2. Robert C Read, professor2,
  3. Richard Amlôt, scientific programme, leader3,
  4. Tim Chadborn, head of group4,
  5. Cathy Rice, public contributor5,
  6. Jennifer Bostock, research adviser6,
  7. Lucy Yardley, professor7 8
  1. 1Primary Care Population Sciences and Medical Education Unit, Faculty of Medicine, University of Southampton, Southampton, UK
  2. 2NIHR Southampton Biomedical Research Centre, University Hospital Southampton, Faculty of Medicine and Institute for Life Sciences, University of Southampton, Southampton, UK
  3. 3Behavioural Science Team, Emergency Response Department, Public Health England, London, UK
  4. 4Behavioural Insights, Public Health England, London, UK
  5. 5Bristol, UK
  6. 6Nuffield Department of Population Health, University of Oxford, Oxford UK
  7. 7Department of Psychology, University of Southampton, Southampton, UK
  8. 8School of Psychological Science, University of Bristol, Bristol, UK
  1. Correspondence to: P Little p.little{at}soton.ac.uk

Paul Little and colleagues call for better promotion of simple measures that can help reduce the spread and severity of infection among those living with people who have covid-19

Most people with covid-19 are cared for at home, increasing the likely exposure of household members. Although the evidence is limited, high infection rates among health workers have been attributed to more frequent contact with infected patients, and higher viral load —the size of the infecting dose of virus. This has led to demands for better personal protection equipment (PPE). Less attention, however, has been given to family members and others caring for people with covid-19 in the community. Providing them with the same level of PPE as in hospitals is not practicable, but promotion of simple evidence based interventions may lower the risk of infection transmission and help reduce morbidity and demand on hospitals.

Transmission in home and community

The long incubation and high presymptomatic infectivity of covid-19 makes transmission between family members a particular risk. Modelling of viral shedding in 94 patients with covid-19 and 77 transmission pairs suggests that the highest viral load is at or just before symptom onset, with 44% of transmission occurring before symptoms.1

Public health advice recommends isolation of symptomatic household members, but this can be difficult, particularly in small flats with shared facilities. Motivation to overcome these difficulties may not be high enough if members of the public are sceptical about reducing transmission in the home and unaware that the illness of other family members may be more severe if they do not reduce their level of exposure.

The medical community is commendably reluctant to make recommendations in the absence of evidence. An expert team that reviewed the evidence for viral load concluded that until the evidence is more conclusive: “As our grandfathers used to say, when …

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