Overview

You may have heard of this disease a lot, or you might have personally encountered the infection before (me, for instance). Most people might think of it as a practically harmless and very common lung infection, and that is the biggest misconception ever. 

Pneumonia describes an inflammation in the lung, primarily in the alveolar space, which results in various symptoms and is mainly characterised by the collection of mucus in the lungs. Pneumonia can be caused by infections by bacteria, fungi, viruses, etc., but in this article, we will focus on bacterial pneumonia, typically caused by Streptococcus pneumoniae, Staphylococcus aureus and many more. Persistent inflammation induced by the infection can leave permanent damage to the lungs, resulting in gaseous exchange disruptions, potentially ending up with respiratory failure. It is essential to understand the long-term disastrous impact pneumonia can have on an individual so that efficient management of the disease can be executed, thereby contributing to lowering its incidence among the global population. 

What is bacterial pneumonia? 

Bacterial pneumonia, as the word implies, is a bacterial infection in the lungs. Our lungs and respiratory tract are consistently exposed to a diverse population of microbiota carried by inhaled air from the environment. The theory of the lungs being a sterile environment, as documented in textbooks, no longer holds valid.¹ With that being said, our immune system plays a vital role in keeping the pathogen load as low as possible by controlling the proliferation rate of microbiotas under normal circumstances. The host defence mechanisms include the regular beating of cilia, mucus, surfactant proteins, and immune responses that keep bacterial growth under control in healthy individuals.^2,3 However, when the host immune system collapses or the pathogenic bacteria overthrow the host’s defence mechanism, inflammatory events will be triggered in response to the bacterial invasion, leading to bacterial pneumonia.³  

The alveolar macrophages are the primary defence unit against bacteria invasion. These macrophages react by releasing a range of pro-inflammatory cytokines to eliminate the bacteria and prevent them from spreading.³ Despite that, these cytokines act as a double-edged sword. While the cytokines are doing their job, initiating a series of immune responses to fight the bacteria, the alveoli are also affected by the inflammation, resulting in alveolar walls being damaged. These leaky alveolar walls promote the accumulation of pus (formed by the collection of dead immune cells in response to an infection) in the alveoli, consequently leading to reduced lung compliance and other clinical presentations of bacterial pneumonia.⁴

Depending on the severity and type of pneumonia, affected individuals can be hospitalised or non-hospitalised. The CURB-65 severity score is used to determine whether hospitalisation is necessary or whether intensive care is required.³ Treatment aims to prevent complications such as sepsis and meningitis while also healing the infection.² Symptoms of the disease generally go away within two to four weeks, but prolonged treatment will be needed for more severe cases. 

What are the immediate effects of pneumonia?

Clinical symptoms of pneumonia also differ depending on the severity of the disease. Some of the common manifestations of pneumonia include: 

• Fever and chills
• Cough (or chesty cough with yellow or green phlegm) 
• Headache 
• Fatigue 
• Chest pain
• Feeling nauseous, vomiting
• Loss of appetite 
• Wheezing (primarily in younger individuals) 

Severe cases of pneumonia, primarily in older individuals, may develop dyspnea (shortness of breath), confusion and complications such as multi-organ failure, sepsis, meningitis and empyema.^2,3

The diagnosis of pneumonia involves a range of tests to evaluate the functioning of the lungs. For instance, the CURB-65 evaluation takes into account several parameters, including the respiratory rate, to determine the severity and the need for hospitalisation. A series of pulmonary function tests (PFT) will also be performed to test the respiratory function and contribute to monitoring the progression of the disease over time.⁵ The procedures of PFT include spirometry tests and measurements of lung volume. Besides, affected individuals will have their blood oxygen level tracked at all times using pulse oximetry in case of hypoxia, indicating a severe infection.²

To confirm the presence of inflammation, a complete blood count (CBC) test is conducted to detect elevated levels of inflammatory biomarkers, such as C-reactive protein (CRP) and an elevated erythrocyte sedimentation rate (ESR) in the blood.^2,3 CBC tests are also useful for GPs to monitor persistent inflammation and track the patient's response to treatment, enabling better disease management. 

Long-term impact of bacterial pneumonia on the lungs 

One common complication of severe pneumonia is pulmonary fibrosis. As aforementioned, the release of pro-inflammatory cytokines perforates the alveolar wall, resulting in leaky walls and impaired gaseous exchange. Meanwhile, the cytokines, the alveolar lesions and persistent inflammation induce fibrotic formation, resulting in scarring and thickening of the alveolar tissues.^2,6 Thickened alveolar tissues make it harder for oxygen to diffuse into the bloodstream. Consequently, the affected individual will experience difficulties in breathing and defective oxygen delivery to other organs, especially the brain. Pulmonary fibrosis is a long-term complication that mainly affects people in their 60s and above. The disease generally progresses over time and is currently incurable.

If the infection persists, more pus will be collected in the lungs. Eventually, more harmful bacteria will grow, resulting in repeated infections in the airways. Due to the considerable overlap in the bacteria species causing bronchiectasis and bacterial pneumonia, recurrent infections can cause scarring and permanent dilation in other parts of the airways, particularly the bronchial tree.⁷

Untreated or under-treated pneumonia causes the lungs to continuously be in an inflammatory state, which could lead to permanent damage in the airways, ultimately resulting in more severe, life-threatening complications such as acute respiratory distress syndrome (ARDS) or respiratory failure.⁴

There has always been a significant linkage between chronic obstructive pulmonary disease (COPD) and pneumonia. Studies have shown a greater exacerbation rate of COPD in people with a history of pneumonia.⁸ Similar to pneumonia, COPD is characterised by the production of pus and difficulty in breathing. However, there is no cure for COPD. Pneumonia can sometimes be misdiagnosed as COPD due to its similarity in the symptoms presented. Constant irritation and damage to the lining of alveolar walls caused by prolonged exposure to pathogenic bacterial infection makes the lungs more prone to the development of COPD. This explains why people with a history of pneumonia are more susceptible to developing COPD. This group of people has an increased risk of experiencing rapid progression of the disease, which could result in respiratory failure.⁹

Management strategies for bacterial pneumonia 

The typical therapy for the recovery of pneumonia usually takes up to seven days. Antibiotics are often prescribed, but the type of antibiotic used will depend on the type of bacteria causing the infection. Other over-the-counter medications, such as fever or cough medicines, are also recommended to help ease symptoms and discomfort. 

For hospitalised patients, intravenous (IV) administration of antibiotics and fluids is used as a first-line treatment. The use of corticosteroids and bronchodilators also showed positive results in severe pneumonia cases that require intensive care. Bronchodilator therapy is often given to people with coexisting conditions of COPD and pneumonia to alleviate breathing difficulties by promoting the dilation of airways.² Mechanical ventilators or oxygen therapy may be used in severe cases to stabilise vital signs.

Treatment and management strategies for pneumonia are based on a series of evaluations and assessments that stratify the severity of the infection and determine whether the patient will receive inpatient or outpatient care. Also, routine check-ups and tests (PFT) are crucial to monitor the progression of the disease in provision for the episodes of other respiratory complications that could be life-threatening, especially for high-risk groups, such as infants and the elderly.⁵

Preventive measures

Despite having a considerably high incidence and mortality rate, pneumonia can be prevented through various efforts. Pneumococcus vaccines, influenza vaccines and COVID-19 vaccines should be enforced in all communities, especially for people who are:^2,3

• Aged 65 or older
• Aged two or younger
• Immunocompromised
• Asthmatic 
• HIV-infected
• Smoking individuals 
• Affected with chronic heart or lung diseases 

If you experience any of the symptoms stated above, you should seek medical advice as soon as possible. Delayed treatment can lead to adverse circumstances, resulting in long-term deterioration of the lungs. The earlier the treatment is given, the higher the chances of recovery and the lower the chances of developing respiratory complications. 

Raising public awareness about the nature of the disease is paramount so that people of all ages are aware of the risks and ways to prevent themselves from being infected. Everyone is encouraged to practise good hygiene at all times and refrain from smoking as it promotes the likelihood of being infected and enhances the progression of the disease.²

Summary

Bacterial pneumonia can be mild in most people, but it can also be fatal for infants and older people. The manifestations of the infection can vary vastly from one individual to the other based on the presence of comorbidities, the severity of the infection and individual factors. Therefore, a range of assessments and tests are necessary to come up with the appropriate treatment and management for each patient and decide if intensive care is needed. Regular monitoring is also crucial as the treatment can be prolonged, and it can potentially progress into life-threatening complications. Hence, counselling and education for affected individuals and the public is obligatory so that everyone can take the initiative to ensure their own physical well-being, thus reducing the incidence rate of bacterial pneumonia.