Recent events have shone a spotlight on pneumonia, and sparked a debate as to whether those who develop this condition can be described as medically fit to hold high office.
But what are the realities and risks of pneumonia?
Pneumonia is an acute infection of the lungs. It is diagnosed by symptoms of infection (including a high, or sometimes low, temperature) accompanied by symptoms that suggest the infection heralds from the lungs (including breathlessness, a cough productive of purulent sputum and chest pain) plus indications on chest images that are compatible with infection.
Pneumonia is very common; it affects approximately 400,000 people in the UK each year: it can also be very serious and is the leading infectious cause of death in developed countries. Despite global campaigns to recognise severe infections in patients and initiate early treatment, mortality rates have stubbornly failed to improve over the last decade.
Patients with the poorest prognosis are those who go on to develop sepsis. Sepsis is defined as life threatening organ dysfunction caused by a dysregulated immune response to infection. Here, the body’s own defences harm host tissue and compromise blood flow leading to a low blood pressure, confusion and organ failure. At worst, sepsis progresses into septic shock where the blood pressure remains low and the body’s organs fail despite treatment.
Pneumonia is caused by bacteria invading the lung, but we breathe in bacteria all the time and usually this does not result in infection. Lung tissue is protected by a number of defences, however, once these defences are breached, the body relies on its most abundant immune cell, the neutrophil, to clear infection.
Neutrophils are short-lived cells that are produced in large numbers by the bone marrow, enter the blood stream and, during infection, accurately migrate from the blood into tissues where they clear bacteria by ingesting them. They contain an arsenal of weaponry, including enzymes and reactive oxygen species that are bacteriocidal, perforating the bacterial cell wall and dismantling its internal contents. Proteins released from neutrophils can be damaging to host tissue and therefore our immune system relies on our neutrophils reacting accurately and decisively during invasive infection, then shutting down and being cleared from the tissue, to avoid harm to self.
Pneumonia occurs when our host defences cannot adequately repel infection. This can occur in anyone if the bacteria that enter the lungs are virulent enough. Pneumonia is seen in healthy, young adults and in such cases, although mortality rates are low, deaths still occur.
In many cases, the patient has risk factors that have predisposed them to disease and that are associated with poorer outcomes. These include the presence of lung disease (where inflammation and structural changes to the lung support bacterial invasion), suppression of the immune system (which can occur in common conditions such as diabetes, as a result of some diseases of the bone marrow or blood and as a side effect of some medications), but the most common risk factor is age.
Older people have a greater risk of pneumonia, have a higher burden of sepsis and experience worse outcomes. This is partly because older people are more likely to have the medical conditions that predispose to pneumonia but also because our immune system becomes less effective over time.
Termed 'immunosenescence', by the sixth decade of life there is a progressive decline in how effectively our immune system can target infection and how quickly resultant inflammation can resolve. Our research suggests that neutrophil functions decline with age; less able to reach a source of infection and clear bacteria. This impairment deteriorates further during lung infections including pneumonia until, during sepsis, there is immunoparesis. Here, neutrophils fail to amount an effective response to infection.
However, these findings are not ubiquitous with age. Some elderly people demonstrate immune functions that are more in keeping with those of a much younger person, suggesting it is not our chronological age, but perhaps our physiological age that dictates how well our immune system works. Our research suggests frail older people experience a greater decline in immune function compared with healthy older adults, and that factors such as physical activity may positively impact on our immune system.
In young adults, most cases of pneumonia resolve without any impediment in long-term health. In older adults, recovery can be more complex with evidence of health consequences if pneumonia and sepsis are experienced in old age. Our own research suggests immune function does not fully recover in patients over 60 years of age, even at six weeks following the infective episode. In keeping with this, older pneumonia patients experience high re-infection rates, with up to 30 per cent readmitted to hospital due to lung infections and sepsis. Post-pneumonia, older patients also experience higher rates of cardiovascular disease including heart attacks and strokes, the risk of which persists for a number of years after the infective event. These poor health outcomes are believed to be a by-product of a poorly functioning immune system – part of immunosenescense.
Most bacteria that cause pneumonia can be killed by antibiotics commonly used in clinical practice, and yet people still die with this condition. In light of this, there is a pressing need to identify strategies that can improve how the immune system works in age and during infections before sepsis develops. However, to date, there are no effective treatments that improve immune cell function when severe sepsis is established.
Recent images of Hilary Clinton appear to show her requiring help to stand at a public event, and this could suggest the presence of sepsis alongside the confirmed diagnosis of pneumonia. These images have fuelled speculation as to her health in general.
Mrs Clinton’s chronological age may place her in a category that is more at risk of poor health outcomes following pneumonia compared with a younger adult, but risk is not certainty. Ageing is heterogenous, anyone can develop pneumonia, and although some experience health issues following this condition, many do not. Perhaps the silver lining of this media spotlight might be increased public awareness of pneumonia and increased interest in finding new treatments for this potentially serious condition, which would be of significant global benefit.
Senior Lecturer, The Institute of Inflammation and Ageing, University of Birmingham and Consultant in Respiratory Medicine, Queen Elizabeth Hospital, Birmingham