Burning Down the House: Climate Change Drives Emerging Infections
Still, there are a multitude of contributing factors
There are the related and contributing problems of deforestation, rapid global travel, and the movement of migrant populations, particularly from rural to urban or peri-urban environments, said Caroline Buckee, PhD, professor of epidemiology at the Harvard T.H. Chan School of Public Health.
“If you were going to design a perfect system to spread a pandemic, you would put everybody in very close proximity in cities and then connect them by global travel as much as you can,” she said in a recent webinar at the T.H. Chan School.1 “And that’s exactly what we have. We have people in closer proximity, with environments where we have a huge diversity of potentially zoonotic emergence events. We’ve created a system that is not only driven by climate, it’s also setting us up for increasing and worse pandemics. That’s something I think about a lot.”
Primarily waterborne in coastal seas, Vibrio vulnificus bacterial infections are hardly the stuff of pandemics. But V. vulnificus thrives in warming waters, particularly brackish inner coastal waters and estuaries. There have been fatal infections this year reported as far north as Connecticut and New York.
With warming waters, the waterborne bacteria have steadily extended their habitat northward up the Eastern Seaboard. V. vulnificus infections in the Eastern United States increased eightfold from 1988-2018, and the northern geographic range of infections has increased about 30 miles per year over that period, the Centers for Disease Control and Prevention (CDC) reported. “Amid increasing water temperatures and extreme weather events — heat waves, flooding, and severe storms — associated with climate change, people who are at increased risk for V. vulnificus infection should exercise caution when engaging in coastal water activities,” the CDC advised in a health alert.2
People with liver disease or some other source of compromised immunity are at the highest risk. The infection most often is caused by entering the water with a cut or wound, which can be beset with necrotizing fasciitis, requiring urgent treatment. The infection also can be caused by consuming oysters contaminated with V. vulnificus.
Although this seems a fairly clear example of climate change expanding a pathogen’s habitat to reach new human populations, there is a need for more granularity of data on the issue to truly understand and prevent it. For example, malaria transmission via mosquitos has been strongly linked to deforestation of the Brazilian Amazon.3 The connection is not as clear in Africa, according to another study.4
In any case, deforestation creates encroachment on animal habitats and more likelihood of a “spillover” of zoonotic infections to human populations. “As deforestation happens, humans get closer to this huge reservoir of viruses that are in the forest in different kinds of animal species,” said Marcia Castro, PhD, chair of the Department of Global Health and Population at the Harvard T.H. Chan School of Public Health. “And the possibility of a new zoonosis emerging is also very high. In fact, I think we lucked out that nothing has emerged as a greater problem so far.”
A warming planet and the aforementioned trends extend the range and effect of some pathogens, including those that are vector-borne by mosquitoes and ticks. Still, it is hard to winnow out the converging aspects of the problem, particularly for vector-borne diseases, said Ari Bernstein, MD, interim director of the Center for Climate, Health, and the Global Environment at the Harvard T.H. Chan School of Public Health.
“Lyme disease is in Canada,” he said in the T.H. Chan School webinar. “The ticks that transmit Lyme disease are in Canada. It’s pretty clear that they weren’t there before. People say it’s hard to tease out the human influence, right? So, are we changing the forest ecology to make ticks present? Or are we changing habitats? That is one of the big challenges that makes the crystal ball of climate change and vector-borne disease hard to see through.”
It is important to determine the role of contributing factors so the problem can be fought at its source. But it is difficult to ascribe, for example, the nine locally transmitted malaria cases in the United States this year solely to climate change. “Locally” is the operative word, since about 2,000 cases are diagnosed annually in the United States, but the vast majority are in returning travelers and immigrants from endemic malaria regions in Africa and South Asia.
Seven of the cases of locally acquired malaria occurred in Florida and one occurred in each in Maryland and Texas. “Consider the diagnosis of malaria in any person with an unexplained cause of fever, regardless of international travel history, particularly if they have been to areas with recent locally acquired malaria,” the CDC recommended in a health advisory alert.5
Anopheles mosquitoes can transmit malaria from an infected person to others, but the parasitic disease is not otherwise contagious between humans.
“If you see someone with anemia, fever … now you’ve got to add malaria to the list of differential diagnoses,” said Vincent Hsu, MD, MPH, hospital epidemiologist and director of Infection Prevention at AdventHealth in Orlando. “The risk is low, but we have to keep our clinicians on alert — you have to think about locally acquired.”
‘A Lot of Waste’ in Healthcare
Hsu emphasized the connection between climate change and emerging infections at the 2023 conference of the Association for Professionals in Infection Control and Epidemiology (APIC). He urged infection preventionists to take an active role in this fight, raising awareness of emerging infections and becoming involved in their facilities efforts to reduce carbon emissions.
“I’m a firm believer that healthcare has to be part of the solution,” he said. “We can’t just be treating patients who have climate-change-related diseases. We’ve got to work in our facilities to reduce our emissions. This is something, organizationally, we can do more of together — to look at climate solutions through the lens of diversity, equity, and inclusion.”
Somewhat undermining its central mission, healthcare overall contributes about 8% to 10% of greenhouse emissions in the United States, Hsu said. For example, the anesthetic gas desflurane clearly contributes to global warming by remaining in the atmosphere upon release for more than a decade.6
“There is lot of waste that goes on, we use a lot of anesthesia gases, there’s a lot of single-use plastic devices,” Hsu said. “Advent Health has signed the Department of Health and Human Services’ Climate Change [pledge] that we want to reduce our emissions by 50% and really, ideally, get down to net zero in a matter of years.”7
The Joint Commission took some preliminary steps toward an accreditation standard earlier this year, saying it could no longer ignore hospital contributions to greenhouse gas emissions. “Hospitals need to take action to minimize their carbon footprints as they care for patients. Hospitals can begin decarbonization activities by measuring and reducing their greenhouse gas emissions,” the Joint Commission said.8
However, the accreditation agency ultimately left such efforts voluntary rather than issue a new standard as healthcare delivery is just coming out of the pandemic.
“They got a lot of pushback; maybe now is not the right time. We don’t have enough healthcare workers, for example,” Hsu said. “But believe me, this is going to come back at some point. We want to recognize that this is an area that we need to pay attention to.”
Emily Mediate, director of climate and health at Health Care Without Harm, expressed “deep disappointment” in a statement on the Joint Commission’s decision. Health Care Without Harm is trying to transform the medical sector into a leader in the global movement for environmental health and justice.
“The health and financial impacts being caused by the crisis demand urgency,” she said.9 “We simply don’t have the time for this to be a slow, voluntary effort, especially for those disproportionately impacted by the climate crisis.”
It was not that long ago that the existence of climate change, particularly as a result of human activity, was met with skepticism and outright denial. There still is some resistance to the concept, but from a scientific standpoint, the jury is in. From a dataset of 88,125 climate-related papers published since 2012, when this question was last addressed comprehensively, researchers examined a randomized subset of 3,000 peer-reviewed articles. Only four skeptical papers were found in the 3,000 published articles.
“We conclude with high statistical confidence that the scientific consensus on human-caused contemporary climate change — expressed as a proportion of the total publications — exceeds 99% in the peer-reviewed scientific literature,” the researchers concluded.10
Regarding a future pandemic, Hsu was doubtful that we will see the century of time that lapsed between 1918 influenza and the emergence of COVID-19.
“With COVID, the worst is behind us — I feel very confident about that,” he said. “But we have to recognize that there will be waves of COVID that may come and go. When is the next pandemic going to strike? I mean, unfortunately, I don’t think it’s going to be another hundred years. I think we could probably, easily, could see another pandemic in our lifetime or even in our careers.”
Hsu emphasized the concept of “One Health,” the paradigm that underscores the connections between human behavior, animal populations, and the environment that combine to drive emerging infections.
“We live and die in a One Health world,” he said. “Recognize the role that we play in our behaviors, our attitudes, animals, the environment — everything we do is interconnected with everything else.”
In such conditions, infections not endemic to an area may suddenly appear, while those of familiarity may not follow their traditional seasons. To get a firmer understanding of these phenomena, the climatology data and the medical data ultimately must be linked in some fashion, Buckee said.
“The environmental data are available on huge spatial scales or [they are] from climate models,” she said. “And the resolution of the data isn’t fine enough in order to be able to link it meaningfully with health data.”
Infection control and healthcare epidemiology can play important roles in pathogen surveillance, raising public awareness, and educating healthcare workers.
“I don’t want to have to add something else to the plate, but this is something that IPs [infection preventionists] have a responsibility to deal with,” Hsu said. “I recognize that not every emerging infectious disease is going to become a pandemic, but we have to recognize that the more emerging infections that you see, the greater the likelihood that one of them could be widespread.”
In that regard, Hsu cited recent events, such as the unusual appearance of a vaccine-derived strain of polio in New York, the dramatic emergence and spread of mpox (monkeypox), and the global spread of Candida auris as a nosocomial pathogen since its emergence in Japan in 2009.
“One of the big concerns is that C. auris was driven or escaped out of the environment partly due to the warming Earth,” Hsu said. “There is no doubt — the science is clear — that climate change is a driving force for emerging pathogens.”
IPs do not have to master all the nuances of climate change and emerging infections, but it would be wise to establish knowledgeable contacts in this area. “If you are not necessarily an expert in emerging infectious disease, you don’t have to be,” Hsu said. “The most important thing is to know where to look, know where to go to access those resources. You can build relationships. Try to identify people who you know who have that [information]. If it’s important, you should hear about it.”
A broader index of suspicion for emerging infections can be seen as part of the critical infection control mission to “identify, isolate, and inform,” Hsu said.
He encouraged APIC attendees to get involved in their facilities climate mitigation efforts, but conceded some may be more drawn to other issues, such as improving vaccine uptake or antibiotic stewardship to prevent drug-resistant bacterial infections.
“Talk to your leadership,” he said. “Maybe you already have a sustainability committee, and if you’re interested in that, you can certainly join. I’m a member of mine.”
- YouTube. Confronting the link between climate change and infectious diseases. May 8, 2023. Harvard T.H. Chan School of Public Health. Published May 19, 2023. https://www.youtube.com/watch?v=RdqZIrySRkE
- Centers for Disease Control and Prevention. Severe Vibrio vulnificus infections in the United States associated with warming coastal waters. Published Sept. 1, 2023. https://emergency.cdc.gov/han/2023/han00497.asp
- MacDonald AJ, Mordecai EA. Amazon deforestation drives malaria transmission, and malaria burden reduces forest clearing. Proc Natl Acad Sci U S A 2019;116:22212-22218
- Bauhoff S, Busch J. Does deforestation increase malaria prevalence? Evidence from satellite data and health surveys. World Development 2020;127:104734.
- Centers for Disease Control and Prevention. Important updates on locally acquired malaria cases identified in Florida, Texas, and Maryland. CDC Health Alert Network Published Aug. 28, 2023. https://emergency.cdc.gov/han/2023/pdf/CDC_HAN_496.pdf
- Wen LS. Health care itself is worsening climate change. One small switch can help. The Washington Post. Published April 5, 2023. https://www.washingtonpost.com/opinions/2023/04/05/health-care-climate-change-desflurane-anesthetic/
- U.S. Department of Health and Human Services. Health sector commitments to emissions reduction and resilience. Last reviewed July 20, 2023. https://www.hhs.gov/climate-change-health-equity-environmental-justice/climate-change-health-equity/actions/health-sector-pledge/index.html
- The Joint Commission. Comment on proposed new requirements to address environmental sustainability. Published March 22, 2023. https://www.jointcommission.org/resources/news-and-multimedia/newsletters/newsletters/joint-commission-online/march-22-2023/comment-on-proposed-new-requirements-to-address-environmental-sustainability/#.ZDg-enbMJD9
- Health Care Without Harm. Health Care Without Harm urges Joint Commission to make sustainability standards required. Published April 28, 2023. https://noharm-uscanada.org/articles/news/us-canada/health-care-without-harm-urges-joint-commission-make-sustainability#:~:text=April%2028%2C%202023-,Health%20Care%20Without%20Harm%20urges%20Joint%20Commission%20to%20make%20sustainability,from%20the%20health%20care%20community
- Lynas M, Houlton BZ, Perry S. Greater than 99% consensus on human caused climate change in the peer-reviewed scientific literature. Environ Res Lett 2021;16:114005. https://iopscience.iop.org/article/10.1088/1748-9326/ac2966
The connection between emerging infections and climate change has gone from theoretical discussions in the past few years to an evidence-based phenomenon happening in real time. That said, there are multiple converging factors, and attributing all emerging infections to global warming is too broad a stroke to explain a complex issue.
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