Overview

Bacterial pneumonia is an infection caused in the lung by bacteria. The pathogen often leads to inflammation of the lung tissues as well as fluid buildup in the lungs, causing its common symptoms of difficulty breathing and coughing up mucus or even blood. It is a dangerous disease, especially in those who are immunocompromised as they struggle more to fight off the infection. Therefore, it is critical for those with weakened immune systems to take extra care in preventing the onset of bacterial pneumonia. 

Risk Factors

Causes of Weakened Immune Systems

The weakening of the immune system may be a result of multiple different conditions. It is a common consequence of:

• Chronic illness. This includes conditions such as HIV infection/AIDS. HIV is a virus, which invades and damages CD4 T cells, which are important players in immunity. These cells are key in recruiting other parts of the immune system, making them the coordinators of immune responses. Without these cells, the body has a lot more difficulty protecting itself, allowing the development of more serious infections. 
• Use of immunosuppressive drugs. Drugs like this are often given to organ transplant patients to decrease the immune response to prevent rejection of the new organ. This can pose a problem when someone is exposed to infectious agents, as since their immune response has been dampened, they are more likely to experience more grave consequences of infection. (e.g., chemotherapy, corticosteroids). A similar notion is also true for cancer therapies such as chemotherapy or radiation. These may lead to a decreased number of white blood cells, which are key immune components, again increasing the likelihood of severe infection. 
• Age-related immune decline. Many times, elderly patients produce fewer B and T cells in their thymus and bone marrow, therefore reducing the effectiveness of their immune system. These cells are key in fighting infection with B cells producing antibodies, and T cells killing infected cells directly. This is also furthered by the fact that a majority of older patients suffer from other comorbidities such as heart disease, which further takes a toll on immune system function.  

Common Sources of Infection

There are a few types of pneumonia, that someone may acquire. The first is community-acquired pneumonia, or CAP for short. This type of pneumonia is caught in the general community away from any healthcare setting. The most popular bacterial culprit of CAP is Streptococcus pneumoniae but there are also many cases caused by other bacteria like, for example, Haemophilus influenzae. The other type is hospital-acquired pneumonia abbreviated to HAP. This type of pneumonia, as the name suggests, is one which was caught at the hospital. In hospitals, the presence of antibiotic-resistant bacteria is higher than in the community, and so oftentimes the causative bacteria are resistant, making treatment a lot harder. The most common cause of HAP is methicillin-resistant Staphylococcus aureus (MRSA). Ventilator-associated pneumonia (VAP) is a type of pneumonia possible in healthcare settings in patients connected to a ventilator. The causative bacteria can either be the ones that cause CAP or HAP.^1,2 

Key Prevention Strategies

Vaccination

Pneumococcal vaccines are highly recommended as a preventative strategy against pneumococcal disease. These are administered to babies in two doses. The first dose is given at 12 weeks, and the next booster shot is given when the child is one year old. For adults, a single dose is administered.³ Other vaccines, such as the vaccine against Haemophilus influenzae may also be recommended as this organism is also capable of causing bacterial pneumonia. Furthermore, receiving the annual influenza vaccine is also recommended for immunocompromised individuals. This is because respiratory infections caused by the influenza virus are very common and may lead to secondary bacterial pneumonia. Therefore by preventing oneself from catching the flu in the first place, one also decreases the risk of developing bacterial pneumonia. An important point to note regarding vaccines is that live attenuated vaccines, such as the influenza intranasal vaccine, should be avoided in immunocompromised individuals due to the higher risk of developing the actual infection.⁴

Good Hygiene Practices

As the pathogens, which cause bacterial pneumonia may spread from person to person via direct contact or by touching contaminated surfaces. When infected people cough, they release droplets containing the pathogen into the air. These droplets may then be breathed in by someone else or may settle on a surface that others may touch. Therefore, keeping good hygiene is important for preventing bacterial pneumonia. Good hygiene practices include washing the hands regularly with warm water and soap or using a 70% alcohol hand sanitiser if washing is not available. This is especially important before eating or touching the face in case a contaminated surface has been touched. It is also a good idea to regularly disinfect surfaces, which are touched often.  It is also important to have good respiratory hygiene, which involves covering the mouth when coughing or sneezing with a tissue and then disposing of it safely. One should also avoid sharing bottles or utensils with other individuals. 

Avoidance of Crowded and Polluted Areas

Immunocompromised individuals may also consider avoiding crowded and polluted areas. Crowded areas expose individuals to a higher number of people, which increases the probability of catching some type of respiratory infection that may then develop into secondary pneumonia. Also, polluted areas expose the lungs to irritants, which will decrease lung health, making them more susceptible to infection. 

Healthy Lifestyle Habits

Way of life may also have an impact on the immune system and so it is key to make good choices that will maximise immune function. This includes eating well, getting regular exercise (but not overworking oneself), and enough sleep. Smoking and alcohol should be avoided as they seem to have a suppressive effect on the immune system. Smoking also has a direct impact on the lung tissues, causing damage, which makes the lungs more susceptible to infection.^1,5

Medical Management for High-Risk Individuals

Prophylactic Antibiotics 

In some cases, a doctor may decide to prescribe antibiotics without a bacterial infection being established. This is more of a preventative approach, which aims to prevent the infection from establishing rather than treating an existing infection. For example, HIV patients with a T cell count below a certain point may be given trimethoprim/sulfamethoxazole antibiotics as a prophylactic treatment. 

Immune-Boosting Therapies

Another approach may involve targeting the immune system itself rather than the pathogen. In this case, the therapy aims to improve immune system function to increase the chance of the body successfully fighting off the infection. This may be used in, for example, cancer patients experiencing neutropenia, which is when the patients have low levels of neutrophils (a type of white blood cell). These patients may be given granulocyte-colony stimulating factor, G-CSF for short, or filgrastim, which will boost neutrophil production, and so increase neutrophil counts.

Avoidance of Immunosuppressive Drugs (if possible)

In some cases, the use of immunosuppressive drugs, like glucocorticoids will be decided against for certain patients. In this case, the disease treated by the immunosuppressants is most likely less serious than any potential infection, like bacterial pneumonia, that could occur as a result of the use of an immunosuppressant in an immunocompromised individual. Therefore, in these situations the immunosuppressive drugs may be deemed unnecessary and so avoided.^3,6

Summary

Bacterial pneumonia is an infection of the lungs, which may cause grave consequences in immunocompromised patients. Therefore, those with a weakened immune system are encouraged to take preventative measures to decrease the risk of exposure to and infection by pathogenic bacteria. Some preventative measures include vaccination, good hygiene, avoidance of crowds, and healthy lifestyle choices. There are also some medical interventions for bacterial pneumonia prevention, which include prophylactic antibiotics, therapies which aim to boost immune function, and the avoidance of unnecessary immunosuppressant use. 

FAQs

What organism is most likely to cause pneumonia in an immunocompromised host?

The most common organism to cause community-acquired pneumonia in an immunocompromised host is Streptococcus pneumoniae. For hospital-acquired pneumonia, it would be methicillin-resistant Staphylococcus aureus, also known as MRSA. 

Why are people with a compromised immune system at risk for pneumonia?

People with a compromised immune system are at risk of pneumonia due to a weaker immune defence. As their immunity is weaker, they are less likely to clear the causative pathogen, increasing their chance of developing pneumonia.

Do antibiotics work for immunocompromised people?

Mostly yes, antibiotics should work for immunocompromised people. However, it may be possible that the antibiotics used may need to be stronger, have a longer course or be more broad spectrum in immunocompromised individuals. This is because oftentimes antibiotics aid the immune system in infection clearance, but for immunocompromised individuals, this may be a bit more tricky considering the weaker immune function. Furthermore, immunocompromised individuals may be more at risk of infection by antibiotic-resistant bacteria which would require more specialised antibiotics.