The UK government yesterday announced a far-reaching package of social distancing measures to suppress the spread of COVID-19. These are based on some Imperial College London modelling work, published here. The model predicts that the UK approach to mitigate the impact of the UK epidemic would indeed reduce the overall number of people affected and those who die, but would still leave hundreds of thousands dead in an overwhelmed healthcare system. In contrast, a more intensive suppression approach would be effective in reversing the epidemic trend and keep the number of new cases to a low level – in the short term, at least.
I recently came across a fascinating review article published in 1963 mainly about outbreaks of Salmonellosis during the 1950s. The review focuses on epidemics that were traced to contaminated surfaces, including ingested, contact and inhaled transmission routes. A number of interesting epidemics stand out:
- An outbreak linked to contaminated neonatal respirators.
- An outbreak linked to a contaminated chopping board (see Figure). In this outbreak, one of the investigators apparently contracted Salmonellosis after touching the chopping board during sampling and then having a cigarette before washing his hands.
- An outbreak (of microbial endotoxin syndrome) linked to a contaminated mouthpiece of SCUBA equipment. Here, the outbreak occurred in naval diving academy and the pattern of lessons and cases was so regular, that the epidemiologist could predict precisely when to visit to see the next case.
Figure: A chopping board at risk of persistent microbial contamination due to surface damage.
Although most outbreaks covered in the review relate to ancient catering-related outbreaks of Salmonella, there may be some useful learning for hospital epidemiology today, specifically CRE. It’s rare although not unheard of to find Salmonella carrying a carbapeneamase (i.e. Salmonella CRE). However, Salmonella is a member of the Enterobacteriaceae, so the involvement of contaminated surfaces during outbreaks of Salmonella suggests that contaminated surfaces may also be important during outbreaks of CRE.
It’s interesting that even back in the 1960s contaminated surfaces were recognized as potentially important in epidemics, whereas by the 1980s, the role of contaminated surfaces in endemic transmission was considered negligible. It’s difficult to know whether experts of the 1960s (perhaps there are some reading this?) would have considered contaminated surfaces important in both epidemic and endemic transmission? I suspect so, and we just lost sight of that in the 1980s and 90s.
Image: Ben Hosking.