Pathogens that cause waterborne and foodborne infections include viruses, bacteria, and parasites. I won't read through the list, you could take a look at it while I continue to speak. The relative importance of pathogens that cause these diseases varies regionally, and mainly waterborne and foodborne infection cause diarrheal diseases although not exclusively. This table shows estimated diarrheal deaths in the world in 2013 by pathogen. What's most notable is that in the majority of cases the pathogen is unknown. Also notable is there's more than a one and a quarter million deaths are estimated. So it's a major cause of death in the world. It's mainly a cause of death among children. So it's the fourth leading cause of death among children less than five years of age. In 2013, waterborne infections in the United States are quite common. This is the estimated number, total of almost 20 million per year. So what about climate change and waterborne infections? So increased temperature, extreme precipitation, and frequency or intensity of extreme weather events will lead to increased incidence of waterborne infections. So that's the bottom line. We're going to spend a fair amount of time now looking at the details. So first, temperature. Temperature affects the distribution and survival of pathogens, and pathogens generally reproduce faster at higher temperatures. This slide shows a systematic review and meta-analysis that was performed of ambient temperature in diarrheal diseases. So let's walk through this slide. So first, in the first column here, they divided up the studies that were included in the meta-analysis according to pathogen. So 30 were bacterial. They focused on, but 30 studies focused on bacterial pathogens, eight in viral and 10 didn't distinguish what type of pathogen, it was "all-cause." In the meta-analysis, I calculated a pooled incidence rate ratio and 95 percent confidence interval. For bacteria, it was 1.07 and for all-cause, it was 1.07 quite similar with fairly tight confidence intervals. For viruses, it actually ended up being not significant, although I could tell you that there are some good studies of specific viral waterborne diseases or infections that convincingly show a relationship with temperature. So let's interpret these incident rate ratios. What is 1.07 mean? It's per one degrees centigrade increase in either the mean minimum or maximum temperature depending on the study. So some studies might have used mean, some might have used maximum, etc. that were included in the meta-analysis. So how do we interpret that per one degrees centigrade increase? So it's multiplicative. So if we wanted to know about, what would be the rate ratio for a two degrees centigrade increase? It would be 1.07 times one squared or 1.14. If we want to know the pooled incident rate ratio per three degrees centigrade increase, it'll be 1.07 cubed or 1.23. If we want to look at a 10 degrees centigrade increase, it would be about 1.97 or 2. Meaning that a 10 degrees centigrade increase in ambient temperature would result in about a two-fold increase in diarrheal diseases. So we dealt briefly with temperature, now let's look at storms extreme precipitation and floods in relation to waterborne infections. So number 1, I'm not going to show these data, but take my word for it. These events have been epidemiologically linked to waterborne infections. Let's focus on the mechanism. So first, we could have disruption of water treatment and sanitary Infrastructure. One of the specific concerns is combined sewer overflow which I'll get back to. Second, we could have spread of sewage in areas with disrupted, poor, or no sanitary infrastructure. Third, we could have run off from fields containing animal waste. So all of these factors could result in contamination of waterways, lakes, rivers streams, beaches, or drinking water sources then leading to the waterborne infections. We also could have direct human exposure to contaminated floodwaters. Finally, poor sanitation and unsafe drinking water in shelters and camps for displaced populations could lead to waterborne infections. So here's an example. So you see this man in West Virginia standing in the floodwaters in June 2016. Those floodwaters could very well be contaminated with pathogens from sewage or from animal waste that could be spreading disease and you can see how people get exposed to that during floods. Okay. I said I'd come back to combined sewer systems and combined sewer overflow. So a lot of you probably know how these works but let me go through it for those of you who don't. So a lot of urban areas especially in the United States have combined sewer systems. So that means that you have the waste which includes sewage from homes and businesses going into the pipes. The same pipes are used to collect storm drains, so they used to collect stormwater. So they all mix together, and there's a control device that's here and diverts the water to the sewage treatment plant, and under usual conditions that works fine. On the other hand, if there's too much stormwater, this controlled device could be overwhelmed by the volume of stormwater and not be able to divert all of the stormwater, which also remember, includes sewage to the water treatment, to the sewage treatment plant. Then we have the combined sewage overflow, so this waste just goes out this other drain untreated into wherever it's going streams, rivers, lakes, etc. So when that happens, that means that there's a danger of waterborne infections because of the combined sewer overflow. I think it's relevant to point out the possibility of an interaction between climate change plus we know because of climate change, there will be more intense hurricanes, there'll be more extreme precipitation events, there'll be more flooding, and there'll be interaction between that and deteriorating urban sanitary infrastructure if we allow our infrastructure to continue to deteriorate and that could lead to increased incidence of waterborne infections.
