Pneumonia (Lung infection): Its Causative agents, Prevention and Treatment

Key Facts about Pneumonia:

• It is a lung infection that causes inflammation and the filling of air sacs (alveoli) with fluid and pus, hindering normal oxygen exchange. 
• Infection can be caused commonly by bacteria and viruses and sometimes by fungi, or parasites.
• Common symptoms include cough, fever, chest pain, shortness of breath, and fatigue.
• High Risk for individuals with very young or old age, a weakened immune system, and chronic diseases (e.g., diabetes).
• Spread through respiratory droplets of infected person caused by coughs or sneezes.
• Diagnosis by chest X-rays, pulse oximeter (oxygen level), sputum cultures and blood test.
• Prevention by Pneumococcal vaccine, face mask and adopting good hygiene practices.
• Treatment varies based on pneumonia cause: Antibiotics for bacterial, antivirals for viral, with supportive care to manage symptoms.

What is pneumonia?

Pneumonia is a respiratory disease of the lungs caused mainly by bacterial or viral infections. All kinds of infections are known to cause inflammation and fluid accumulation at the site of infection, which may not pose much harm. However, lung infections lead to the inflammation of alveoli (small pockets in the lung holding air) and the accumulation of fluid, pus, and blood, inhibiting oxygen and carbon dioxide exchange. This causes breathing difficulties, coughing, chest pain, and impaired respiratory function. If left untreated, it may result in death.

Infected Lungs

History

Pneumonia was one of the leading causes of death worldwide up to the early 1900s. The major reason was the bacterium Streptococcus pneumoniae, discovered in the saliva of an infected person by microbiologists Louis Pasteur and George Sternberg in 1880

Streptococcus pneumoniae

It is a Gram-positive, facultative anaerobe also called pneumococcal bacteria. These bacterial strains have a thick outer layer of a polysaccharide capsule that protects the bacteria from the immune system, making them more pathogenic (disease-causing).

Sulfapyridine was the first antibacterial drug used as an anti-pneumococcal in 1939, but soon the bacteria started showing resistance against the drug. Fortunately, the antibiotic penicillin, discovered in 1928, worked successfully against Streptococcus pneumoniae for the treatment of pneumonia. However, the overuse of penicillin led to the existence of penicillin-resistant strains of Streptococcus pneumoniae.

Now a days, various new drugs are being used as anti-pneumococcal, such as Fluoroquinolones, Macrolides, and Tetracyclines. However, recently many pneumococcal bacterial strains have been observed (more than 30% of infected cases) against which these new drugs are also not working. The reasons for this resistance are the unnecessary use of antibiotics and limited use or non-availability of vaccines in developing countries.

Today, there are more than 90 known strains of Streptococcus pneumoniae, and some among these are capable of causing serious infections. The most recent data disclose that every day, around 2000 children under the age of five years are dying due to pneumonia. So, it is very important to provide vaccine to every child around the world.

The first vaccine against bacterial pneumonia was developed in 1977, called PPV, which stands for Pneumococcal Polysaccharide Vaccine. However, it was active against only a limited number of Streptococcal strains. Now a days, the Pneumococcal Conjugate Vaccine (PCV 13) and Pneumococcal Polysaccharide Vaccine (PPSV23) are mostly in use. These vaccines contain polysaccharide antigens from different strains of pneumococcal bacteria, which helps to produce protective immune cells (memory B-cells) in the body. These B-cells protect by producing antibodies when body encounters infection by different strains of Streptococcal bacteria. 

  

         

Vaccines for prevention

Difference between Bacterial and Viral Pneumonia

	Differences
	Bacterial Pneumonia	Viral Pneumonia
Causative agents	Mainly by S. pneumoniae, apart from this Mycoplasma pneumoniae, Klebsiella pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and Pseudomonas aeruginosa.	Mostly by Respiratory syncytial virus (RSV), Influenza virus and Coronaviruses such as SARS-CoV-2
Symptoms	Can be sudden and more severe like High fever with chills, productive cough with greenish and yellow sputum and rapid breathing	Appears gradually including fever, dry cough, muscle aches, difficulty in breathing, sometimes diarrhea and nausea.
Clinical presentation	Generally involved one or more lobes of lungs filled with fluid or solid mass.	Spread over multiple areas of one or both the lungs.
Group at risk	More common in older adults with weak immune system or suffering from chronic lung disease	Affects individuals of all ages but poses risk to elderly, young children, and individuals with weakened immune systems.
Complications	Respiratory failure and septicemia or blood poisoning due to spread of bacteria or its toxins	Viral infection may lead to secondary bacterial pneumonia and become severe
Treatment	Using Antibiotics after checking resistant profile and care to manage symptoms	Using Antiviral drugs which may or may not work and including supportive care
Vaccination	PCV 13 and PPSV23 vaccines	Influenza vaccine or recently developed Corona vaccines

In China, Mycoplasma pneumoniae is currently (2024) a predominant causative agent of pneumonia in children. Mycoplasma pneumoniae can cause respiratory infections by damaging the lining of the respiratory system. Despite being an infection, it is often less severe, hence termed 'walking pneumonia.' Individuals infected with Mycoplasma pneumonia can typically continue their daily activities. This type of pneumonia is more common in children, young adults, and individuals with compromised immunity. This bacterium lacks a cell wall, rendering those antibiotics ineffective, which primarily kill microbes through inhibiting cell wall synthesis. Therefore, commonly prescribed antibiotics to target this bacterium include macrolides (azithromycin) or tetracyclines (doxycycline). These antibiotics kills bacteria by inhibits their protein synthesis.

Fungal pneumonia

It is not a common form of infection as it mostly affects people having low immune status such as AIDS patients or individuals undergoing immunosuppressive therapy and symptoms appear gradually over weeks to months. The most common fungus causing pneumonia is Pneumocystis jirovecii or Pneumocystis carinii. Other fungi include of Genus Coccidioides, Histoplasma and Blastomyces and these fungi are normally present in soil, bird droppings or rotten woods. Spores of the fungi get inhaled leading to severe infection and colonization in lungs of immunocompromised patients.

Fungus in Lung fluid

 Spread

Primary mode of transmission in all the above different types of pneumonia is by direct exposure to respiratory droplets expelled by an infected person through coughs or sneezes or touching surfaces contaminated with the droplets.

Pneumonia can be acquired during a hospital stay through contaminated equipment, healthcare personnel or through contaminated ventilator in severally ill patients.

Preventive measures:

• Ensuring that children receive routine vaccinations including bacterial and viral vaccines.
• Maintain good respiratory health by avoiding pollution and tobacco smoking.
• Maintaining strong immunity with proper nutrition, regular physical exercise and avoiding alcohol consumptions.
• Avoiding direct contact with infected patients, using face masks and proper hand sanitization.  

Diagnosis:

Physical inspection based upon symptoms, medical history and use of stethoscope to hear crackling/abnormal breathing sounds in chest. 

Physical inspection 

Chest X-ray with opaque white spots or area indicating inflammation, fluid accumulation or condensed mass interpreted by certified radiologist or doctor. 

Chest X-ray with opaque white spots 

Blood tests include elevated white blood cell (WBC) count indicating infection, C-reactive protein (CRP) suggest inflammation, increased Procalcitonin (PCT) levels indicate bacterial pneumonia and serological test for viral infection.

Sputum test: Mucus coughed up from the respiratory tract (sputum) is used to grow the bacteria on culture medium and identified using microscopy, biochemical tests, or PCR test. This test is important to decide specific type of antibiotic that can be given for treatment of Pneumonia.

Sputum sample

 

Treatment

The treatment of pneumonia depends on type of infection or type of causative agent i.e., bacterial, viral, fungal or parasitic. It also depends on severity of symptoms and the overall health of the individual. 

Bacterial Pneumonia: Doctors may give antibiotics such as amoxicillin, azithromycin, clarithromycin, and levofloxacin but their use is mostly prescribed after the sputum culture test. This test identifies the causative bacterial strain and after that its resistance profile can be checked. This can help to determine which antibiotics will work against a particular bacterial strain.

Viral Pneumonia: Doctors may give Antiviral drugs such as oseltamivir, zanamivir, and peramivir to control infection caused by Influenza virus. These drugs can prevent spread of virus to surrounding cells by blocking surface proteins of Influenza A and B virus. 

Fungal Pneumonia: Antifungal Medications include trimethoprim-sulfamethoxazole (TMP-SMX) and pentamidine can be effectively used as first line therapy against Pneumocystis pneumonia as per studies.

Supportive Care: Over-the-counter medicines to reduce pain, fever and cough. In severe cases hospitalization may require followed by Intravenous antibiotics or antivirals with oxygen therapy.