Författare: Christine Carson Senior Research Fellow School of Medicine T

Over the past several days, the world has watched on in shock as wildfires have devastated large parts of Los Angeles.

Beyond the obvious destruction – to landscapes, homes, businesses and more – fires at this scale have far-reaching effects on communities. A number of these concern human health.

We know fire can harm directly, causing injuries and death. Tragically, the death toll in LA is now at least 24.

But wildfires, or bushfires, can also have indirect consequences for human health. In particular, they can promote the incidence and spread of a range of infections.

Effects on the immune system

Most people appreciate that fires can cause burns and smoke inhalation, both of which can be life-threatening in their own right.

What’s perhaps less well known is that both burns and smoke inhalation can cause acute and chronic changes in the immune system. This can leave those affected vulnerable to infections at the time of the injury, and for years to come.

Burns induce profound changes in the immune system. Some parts go into overdrive, becoming too reactive and leading to hyper-inflammation. In the immediate aftermath of serious burns, this can contribute to sepsis and organ failure.

Other parts of the immune system appear to be suppressed. Our ability to recognise and fight off bugs can be compromised after sustaining burns. Research shows people who have experienced serious burns have an increased risk of influenza, pneumonia and other types of respiratory infections for at least the first five years after injury compared to people who haven’t experienced burns.

Wildfire smoke is a complex mixture containing particulate matter, volatile organic compounds, ozone, toxic gases, and microbes. When people inhale smoke during wildfires, each of these elements can play a role in increasing inflammation in the airways, which can lead to increased susceptibility to respiratory infections and asthma.

Research published after Australia’s Black Summer of 2019–20 found a higher risk of COVID infections in areas of New South Wales where bushfires had occurred weeks earlier.

We need more research to understand the magnitude of these increased risks, how long they persist after exposure, and the mechanisms. But these effects are thought to be due to sustained changes to the immune response.

Microbes travel in smoky air

Another opportunity for infection arises from the fire-induced movement of microbes from niches they usually occupy in soils and plants in natural areas, into densely populated urban areas.

Recent evidence from forest fires in Utah shows microbes, such as bacteria and fungal spores, can be transported in smoke. These microbes are associated with particles from the source, such as burned vegetation and soil.

There are thousands of different species of microbes in smoke, many of which are not common in background, non-smoky air.

Only a small number of studies on this have been published so far, but researchers have shown the majority of microbes in smoke are still alive and remain alive in smoke long enough to colonise the places where they eventually land.

How far specific microbes can be transported remains an open question, but fungi associated with smoke particles have been detected hundreds of miles downwind from wildfires, even weeks after the fire.

Read more:
LA fires: Long-term exposure to wildfire smoke is poorly understood − and a growing risk

So does this cause human infections?

A subset of these airborne microbes are known to cause infections in humans.

Scientists are probing records of human fungal infections in relation to wildfire smoke exposure. In particular, they’re looking at soil-borne infectious agents such as the fungi Coccidioides immitis and Coccidioides posadasii which thrive in dry soils that can be picked up in dust and smoke plumes.

These fungi cause valley fever, a lung infection with symptoms that can resemble the flu, across arid western parts of the United States.

A study of wildland firefighters in California showed high rates of valley fever infections, which spurred occupational health warnings including recommended use of respirators when in endemic regions.

A California-based study of the wider population showed a 20% increase in hospital admissions for valley fever following any amount of exposure to wildfire smoke.

However, another found only limited evidence of excess cases after smoke exposure in wildfire-adjacent populations in California’s San Joaquin Valley.

These contrasting results show more research is needed to evaluate the infectious potential of wildfire smoke from this and other fungal and bacterial causes.

Firefighters may be at risk of infection from exposure to wildfire smoke.
Jae C. Hong/AP/AAP

Staying safe

Much remains to be learned about the links between wildfires and infections, and the multiple pathways by which wildfires can increase the risk of certain infections.

There’s also a risk people gathering together after a disaster like this, such as in potentially overcrowded shelters, can increase the transmission of infections. We’ve seen this happen after previous natural disasters.

Despite the gaps in our knowledge, public health responses to wildfires should encompass infection prevention (such as through the provision of effective masks) and surveillance to enable early detection and effective management of any outbreaks. Läs mer…

A doctor’s visit often ends with you leaving with a pathology request form in hand. The request form soon has you filling a sample pot, having blood drawn, or perhaps even a tissue biopsy taken.

After that, your sample goes to a clinical pathology lab to be analysed, in whichever manner the doctor requested. All this is done with the goal of getting to the bottom of the health issue you’re experiencing.

But after all the tests are done, what happens with the leftover sample? In most cases, leftover samples go in the waste bin, destined for incineration. Sometimes though, they may be used again for other purposes, including research.

Who can use my leftover samples?

The samples we’re talking about here cover the range of samples clinical labs receive in the normal course of their testing work. These include blood and its various components (including plasma and serum), urine, faeces, joint and spinal fluids, swabs (such as from the nose or a wound), and tissue samples from biopsies, among others.

Clinical pathology labs often use leftover samples to practise or check their testing methods and help ensure test accuracy. This type of use is a vital part of the quality assurance processes labs need to perform, and is not considered research.

Leftover samples can also be used by researchers from a range of agencies such as universities, research institutes or private companies.

They may use leftover samples for research activities such as trying out new ideas or conducting small-scale studies (more on this later). Companies that develop new or improved medical diagnostic tests can also use leftover samples to assess the efficacy of their test, generating data needed for regulatory approval.

What about informed consent?

If you’ve ever participated in a medical research project such as a clinical trial, you may be familiar with the concept of informed consent. In this process, you have the opportunity to learn about the study and what your participation involves, before you decide whether or not to participate.

So you may be surprised to learn using leftover samples for research purposes without your consent is permitted in most parts of Australia, and elsewhere. However, it’s only allowed under certain conditions.

In Australia, the National Health and Medical Research Council (NHMRC) offers guidance around the use of leftover pathology samples.

One of the conditions for using leftover samples without consent for research is that they were received and retained by an accredited pathology service. This helps ensure the samples were collected safely and properly, for a legitimate clinical reason, and that no additional burdens or risk of harm to the person who provided the sample will be created with their further use.

Another condition is anonymity: the leftover samples must be deidentified, and not easily able to be reidentified. This means they can only be used in research if the identity of the donor is not needed.

Leftover pathology samples are sometimes used in medical research.
hedgehog94/Shutterstock

The decision to allow a particular research project to use leftover pathology samples is made by an independent human research ethics committee which includes consumers and independent experts. The committee evaluates the project and weighs up the risks and potential benefits before permitting an exemption to the need for informed consent.

Similar frameworks exist in the United States, the United Kingdom, India and elsewhere.

What research might be done on my leftover samples?

You might wonder how useful leftover samples are, particularly when they’re not linked to a person and their medical history. But these samples can still be a valuable resource, particularly for early-stage “discovery” research.

Research using leftover samples has helped our understanding of antibiotic resistance in a bacterium that causes stomach ulcers, Helicobacter pylori. It has helped us understand how malaria parasites, Plasmodium falciparum, damage red blood cells.

Leftover samples are also helping researchers identify better, less invasive ways to detect chronic diseases such as pulmonary fibrosis. And they’re allowing scientists to assess the prevalence of a variant in haemoglobin that can interfere with widely used diagnostic blood tests.

All of this can be done without your permission. The kinds of tests researchers do on leftover samples will not harm the person they were taken from in any way. However, using what would otherwise be discarded allows researchers to test a new method or treatment and avoid burdening people with providing fresh samples specifically for the research.

When considering questions of ethics, it could be argued not using these samples to derive maximum benefit is in fact unethical, because their potential is wasted. Using leftover samples also minimises the cost of preliminary studies, which are often funded by taxpayers.

The use of leftover pathology samples in research has been subject to some debate.
Andrey_Popov/Shutterstock

Inconsistencies in policy

Despite NHMRC guidance, certain states and territories have their own legislation and guidelines which differ in important ways. For instance, in New South Wales, only pathology services may use leftover specimens for certain types of internal work. In all other cases consent must be obtained.

Ethical standards and their application in research are not static, and they evolve over time. As medical research continues to advance, so too will the frameworks that govern the use of leftover samples. Nonetheless, developing a nationally consistent approach on this issue would be ideal.

Striking a balance between ensuring ethical integrity and fostering scientific discovery is essential. With ongoing dialogue and oversight, leftover pathology samples will continue to play a crucial role in driving innovation and advances in health care, while respecting the privacy and rights of individuals. Läs mer…