costs., health economics, Sanitation, Water

The economics of antimicrobial resistance and the role of water and sanitation services

Wastewater treatment plants – hotspots for resistant genes and bacteria?

Seeing a paper published a few weeks ago in Nature Communications (more on that below) reminded me of some reading I did last year on WASH and antimicrobial resistance (AMR), and got me thinking about the economics of this.

What is AMR?

Antimicrobial resistance (AMR) occurs when microorganisms adapt after exposure to antimicrobial drugs (e.g. antibiotics, antivirals).  Microorganisms include bacteria, viruses and parasites. While AMR is not only about antibiotics, that is the area which has garnered the most concern. Why? Because it is potentially terrifying. Imagine if most hospital operations became too risky due to the chance of infection, or if people died from basic diseases once easily overcome.

As Margaret Chan of WHO put it, “AMR threatens the very core of modern medicine and the sustainability of an effective, global public health response to the enduring threat from infectious diseases”. And from 1980s-2000s, there was a 90% decline in the approval of new antibiotics.

Economic analysis of AMR scenarios

For economic analysis of this kind of thing, the problem is uncertainty about costs and consequences. It is hard to assign probabilities to different AMR scenarios, and hard to adequately cost up the potential economic damage. Prominent health economists Smith & Coast found in a 2012 UK-focused review that estimates of the economic burden were surprisingly modest – from £5 to £20,000 in additional hospital costs per patient per episode (driven by methods for incorporating productivity losses) but argued that these had been too simplistic. At a societal level, estimates were far lower than things like cancer and heart disease in the US and UK, so AMR wasn’t prioritised.

In an accompanying BMJ editorial, Smith & Coast suggested that existing cost estimates did not take into account the fact that antimicrobials are integral to modern healthcare. Noting that accurate cost forecasting is near-impossible, they argue that we should view greater investment in preventing AMR as an “insurance policy”.

This reminded me of working on the economic appraisal of WASH in the context of climate change, and the debates about no-regrets / low-regrets adaptation (see p.32 of this). In a another paper I co-authored with Julian Doczi, we considered appraisal options based on the fact that the ‘deep’ uncertainty surrounding future climate scenarios severely weakens the theoretical foundations of cost-benefit analysis. This DFID topic guide on ‘decision-making under uncertainty’ is good at explaining why. It’s the same problem for AMR – there is the potential for catastrophic outcomes with unknown but not-that-small probability. Standard econ. appraisal methods don’t like this at all.

How does WASH affect AMR?

But what has WASH got to do with AMR? This WHO briefing note provides a good overview of the issue. Essentially, water, wastewater and faeces play a key role in the carriage of microorganisms and their genetic material. Water can act as a reservoir of resistant bacteria and exposure routes to humans (and animals).

So there are many ways in which WASH, and water more broadly, could affect AMR. However, there is evidence that wastewater treatment plants (WWTPs) are hotspots for AMR genes and bacteria. This is unsurprising as they bring multiple sources of waste into one place in huge volumes. Landfills and food crops (cf. wastewater irrigation) are also a concern. WHO state that many faecal indicator bacteria, such as E. coli and enterococci, are now resistant to some antibiotics, with some evidence of higher morbidity and mortality as a result.

The study published a few weeks ago tackles an important question in all this. That is, whether increased levels of antibiotic-resistant bacteria in sewage and river water are more a consequence of (A) on-site selection from antibiotic residues in the environment, or (B) contamination by fecal bacteria that just tend to be more resistant than other bacteria. Explanation A would be “worse”, in the sense that it would confirm fears about increasing AMR. Fortunately for us, by looking a specific virus as a marker, they find:

“the presence of resistance genes can largely be explained by fecal pollution, with no clear signs of selection in the environment, with the exception of environments polluted by very high levels of antibiotics from [pharmaceutical] manufacturing, where selection is evident.”

Phew, up to a point. Nonetheless, as one of the co-authors noted, their results do not exclude the possibility that there is gene selection going in in parallel. And it’s only one study. The potential risks linking AMR and WASH remain.

What’s this got to do with WASH economics?

The Smith & Coast work discussed above focuses on the economic burden / damage costing, i.e. what are the costs of inaction. These fall mainly on people’s health and in healthcare services. What would be more important for WASH is an intervention cost perspective. That is, what does a WASH-related bit of the Smith & Coast ‘insurance policy’ look like? What should we be spending money on, in the WASH sector, to reduce risk of catastrophic AMR?

The answer appears to be that we don’t know yet. The WHO briefing note sets out recommendations for risk assessment and risk management and at the policy level, as well as identifying research needs. One thing they recommend we should be doing is identifying and quantifying relevant bacteria as part of existing microbial monitoring. But there’s still clearly a lot we don’t know. It seems less obvious what should be done in the WASH sector, as compared to the health sector. That makes sense given the health sector is the source of antibiotic use while WASH systems and ecosystems are vectors for genes and bacteria. This is one area of water risk that I’m sure we’ll be hearing more about in the years to come.

Once we do know more, and are in a position to be recommending specific investments, my three questions that would need to be asked of any WASH-related insurance policy would be:

  1. Is there is anything the WASH sector could be doing to reduce risk of AMR, beyond fully implementing existing guidelines for water and wastewater management?
  2. What would those things cost?
  3. Would doing them be a good use of resources compared to alternatives, and how uncertain are we about that? [it will be very hard to say because, as discussed above, the damage costs of AMR are highly uncertain].

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