Abstract
The recognition that infectious diseases can potentially increase with changes in the climate
dates back to the 1990s (1, 2). Climate change is and will continue to affect infectious diseases
through diverse and often overlapping ecological, biological and social mechanisms. The effect
of climatic factors on infectious disease is complex. Climate influences ecological factors, such
as the natural environment in which infectious agents live, grow and multiply. Climatic and
ecological factors will affect organisms’ biology (for example, survival, proliferation, serotype
fitness), which may lead to altered pathogen geographical ranges and distributions or the
seasonality of individual pathogens. For example, there may be longer transmission periods
associated with warmer conditions, although colder conditions drive people indoors, which can
also increase the transmission of some respiratory infections during winter. In addition, the
emergence of novel species may be influenced. Climate change may also affect transmission
through impacts on key vectors, such as rodents, changes of impacts on farming and food
production practices or important pathogen transport mechanisms, such as rainfall and wind
contributing to the dispersal of soil organisms and pathogens. Finally, climate change may
affect human behaviour and other social determinants of infectious disease risk: for example,
warmer weather resulting in changed food preparation and consumption patterns, or increasing
countryside visits, in turn increasing the potential exposure to infectious disease hazards (3). In
England, the economic burden from infectious diseases (including costs to the health service,
labour market and to individuals) is estimated at £30 billion annually, dominated by respiratory
and gastrointestinal infections (4). Hence any changes to disease burdens will not only have
public health implications, but also economic impacts.
Changing human behaviour and policy will play an important role in infectious disease risk, both
by mitigating risk or creating new risks. For example, climate change-induced increases in
foodborne disease outbreaks may lead to the development of new regulations that may in turn
help to minimise health burden. Alternatively, efforts to decarbonise will have important
implications for land use and agriculture (see Chapter 14), which could even increase health
risks if new vector habitats (see Chapter 8 for vector-borne diseases) or transmission pathways
are created (5). In future, changes to health associated with climate change in the UK will occur
concurrently with 2 important trends which may influence disease risk. First, the UK population
is ageing: by 2066, there are likely to be an additional 8.6 million residents aged 65 years and
over, comprising 26% of the total population, with the over 85 years age group showing the
fastest increase (6). The rising UK elderly population will make the population more susceptible
to infections, due to lowered immunity or more frequent interactions with healthcare or living in
communal settings, where for example, the potential for person-to-person transmission is
elevated. Second, antimicrobial resistance (AMR) poses a growing threat to human, animal and
environmental health, implying that future impacts may be greater, with 10 million deaths
globally predicted to occur annually by 2050 due to AMR (7). There is emerging evidence
suggesting that AMR may be influenced by climate change: warming temperatures may
accelerate bacterial growth, increase bacterial infection rates, increase the frequency of
infections in healthcare settings and expand geographical distributions (8 to 12). These
processes increase the likelihood of horizontal gene transfer and thus the emergence of
drug-resistant infections. However, the incidence of respiratory infections is higher during winter,
resulting in greater antimicrobial use for treatment, and increasing the risk of drug-resistant
infections developing as a result. In addition, wastewater is a well-known reservoir for
antibiotic-resistance genes, as bacteria can encounter antimicrobial effluent and develop antimicrobial
resistance genes (13, 14). More frequent and intense precipitation and flooding events in future
will likely lead to increased agricultural runoff and pollutants in water, causing bacterial blooms
and further opportunities for antibiotic resistant gene transfer (14, 15). Though details on AMR
and effects on specific pathogenic species are out of the scope of this chapter, they are
important to note as an emerging climate related health risk.
Infectious diseases have been considered in the ‘Health Effects of Climate Change in the UK
(HECC)’ reports since 2002 (16), when infectious disease was mostly covered within the ‘Food
poisoning and climate change’ chapter. This chapter highlighted parts of food chains where
weather may affect the risk of food poisoning (an umbrella term which includes different
foodborne illnesses). In another chapter, the potential for changing ultraviolet light (UV-B) levels
to affect immune suppression and virus activation were discussed, and the report briefly
considered adaptation, highlighting the largely unknown capacity of the population to adapt to a
changing climate. Indirect influences of climate on infectious disease, such as dietary choice
and human behaviour, were briefly mentioned. Integrated assessment models were highlighted
as suitable for modelling the impacts of climate change on infectious diseases. In the 2008
report, ‘food poisoning’ was separated into constituent illnesses, predominantly Salmonella and
Campylobacter (17). The flooding chapter included infectious disease risks, and UK
consequences of climate change impacts on global food prices was also discussed.
By 2012, a wider range of infectious diseases and transmission routes were considered (18).
The water and food chapters were merged, and there was greater emphasis on food as a global
commodity. The impact of the built environment upon the airborne transmission of infectious
diseases was explicitly addressed for the first time, and concerns about UV-B levels affecting
immune suppression remained. The scarcity of data on how climate change may influence
human behaviour, and hence impact disease incidence, was noted. Adaptation and resilience of
the food sector to changing diseases were explicitly considered. The importance of food as a
contributor to greenhouse gas (GHG) emissions was included, alongside the imperative of
ensuring that food associated GHG mitigation measures do not adversely affect food safety. It
highlighted the importance of dietary choice for GHG emissions and noted win-wins from dietary
changes (for instance, lower animal product consumption reduces both GHG emissions and
saturated fat intake). The report recommended that all climate change mitigation policies be
subject to health impact assessment.