Pneumonia a common infection of the lungs

| In Articles | 27th March 2020

Pneumonia is an inflammation of the lung parenchyma caused by bacteria, viruses (for example coronavirus) and fungi.

Pneumonia - infection of lungs that is treated with antibiotics and sometimes patients requires hospitalisation

Common symptoms of pneumonia are: cough (wet or dry), difficulty breathing, increased heart rate, high temperature, fatigue, sweating, shivering, chest pain and loss of appetite.

A short review of the lung anatomy: they represent the major organs of the respiratory system and are divided into lobes. The right lung has three lobes and is slightly larger than the left lung, which has two lobes.

The known types of pneumonia include community acquired pneumonia (CAP), nosocomial/hospital acquired pneumonia and pneumocystis pneumonia (PCP).

Community acquired pneumonia

Through community acquired we understand that the person is not hospitalised or residing in a long term care facility. 

There are 5.6 million cases of community acquired pneumonia annually and 1.1 million require hospitalisation. The mortality rate is 12% and almost half of those are intensive care unit (ICU) patients.

Methods of diagnosing CAP are: chest Xray, bacteriological examination of sputum, pulse oximetry, routine blood testing (complete blood count, basic metabolic panel, liver function tests), arterial blood gas (ABG) test and thoracentesis (if pleural effusion is present).

The chest Xray is a noninvasive procedure which produces images of the lungs, heart, airways, blood vessels and bones of the chest and spine. Pulse oximetry measures a person's oxygen saturation in the blood by placing a clamp-like device on a finger, toe or earlobe.

A complete blood count provides information about the number and size of the red blood cells, white blood cells and platelets (thrombocytes). The basic metabolic panel measures the glucose, electrolyte and fluid balance. Liver function tests are used to diagnose organ damage by measuring the level of enzymes released by the liver. The ABG requires a small amount of blood to be drawn from the radial or femoral artery with a syringe and thin needle to measure the amounts of oxygen and carbon dioxide in the arterial blood. Thoracentesis is an invasive procedure used to remove fluid or air from the pleural space.

Risk factors include: age (children and elderly), environmental exposures (living in a smoking environment, farm animals, air pollution), malnutrition, poor dental hygiene, immunosuppressive therapy, existing respiratory conditions such as chronic obstructive pulmonary disease (COPD) or structural disease of the lung (bronchiestasis, cystic fybrosis).

The most common pathogens are: Streptococcus pneumoniae, Mycoplasma pneumoniae, Haemophilus influenzae, Chlamydia pneumoniae (alone or as mixed infection), Legionella species, Histoplasma capsulatum, Francissella tularensis, Mycobacterium tuberculosis, endemic fungi and respiratory viruses.

The therapy recommended for community acquired pneumonia includes antibiotics such as Azithromycin, Clarithromycin and Doxycycline. The first two belong to a class called New Generation Macrolides. Doxycycline belongs to the Tetracyclines class. Many species of Streptococcus pneumoniae are resistant to Tetracycline and it should be used only if the patient is allergic or intolerant to the New Generation Macrolides.

The duration of therapy is 5-7 days for outpatients, 7-14 days for inpatients (depending on the infectious pathogen) and more than 14 days for chronic steroid users.

Influenza and pneumococcal vaccines are proven to help prevent community acquired pneumonia. The two vaccines are recommended especially for people who are at high risk.

Hospital acquired pneumonia (HAP)

Hospital acquired means that the infection occurred while the patient was in hospital, 48-72 hours post admission. The incidence is 5 to 10 cases per 1,000 hospital admissions. The patients who require mechanical ventilation are at much higher risk.

HAP is the second most common nosocomial (originating in a hospital) infection with a mortality rate of 70%. It increases the length of stay in hospital by 7-9 days.

The most common pathogens infecting patients with mild to moderate HAP with no unusual risk factors and onset of the disease at any time or patients with severe HAP with early onset are: Escherichia coli, Klebsiella, Proteus, Serratia, Hemophilus influenza, Methicillin-sensitive Staphylococcus aureus and Streptococcus pneumoniae. The core antibiotics for the treatment of HAP caused by the infectious agents listed above are: Second Generation Cephalosporins (Cefaclor, Cefuroxime), Third Generation Anti-pseudomonal Cephalosporins (Ceftazidime, Cefoperazone) and Beta-lactamase inhibitors (Clavulanic acid, Sulbactam).

The most common pathogens infecting patients with mild to moderate HAP with risk factors and onset of the disease at any time are: Anaerobes (recent abdominal surgery, witnessed aspiration), Staphylococcus aureus (coma, head trauma, diabetes mellitus, renal failure), Legionella (high dose steroids), Pseudomonas aeruginosa (prolonged ICU stay, steroids, structural lung disease). The core antibiotics for the treatment of HAP caused by the infectious agents listed above are: Lincomycin antibiotics (Clindamycin), Glycopeptide antibiotics such as Vancomycin (until Methicillin-resistant Staphylococcus aureus MRSA is ruled out), Macrolides (Erythromycin) and Antimycobacterials (Rifampin).

Severe HAP can be defined by the following factors: admission to the intensive care unit, respiratory failure, the need for mechanical ventilation, the need for more than 35% oxygen to maintain an arterial oxygen saturation above 90%, multi lobar lung in involvement, cavitation of a lung infiltrate, evidence of severe sepsis with hypotension and/or end-organ dysfunction, requirement of vasopressors for more than 4 hours, urine output less than 20ml per hour and acute renal failure pending dialysis.

The most common pathogens infecting patients suffering from severe HAP with risk factors and early or late onset of the disease are: Pseudomonas aeruginosa, Acinetobacter species and MRSA. The core antibiotics for the treatment of HAP caused by the infectious agents listed above are: Aminoglycosides (Gentamicin), Fluoroquinolones (Ciprofloxacin), Antipseudomonal penicillin such as Carboxypenicillins (Carbenicillin), Third-generation Cephalosporins (Ceftazidime, Cefoperazone), Carbapenem antibiotics (Imipenem), Monobactams (Aztrenoam) and Glycopeptides (Vancomycin).

The main reasons for therapy failure are: incorrect diagnosis, pathogen resistance, host factors that increase mortality (age, prior pneumonia, chronic lung disease, immunosuppression) and antibiotic resistance.

HAP can be prevented through: hand washing, vaccination (influenza and pneumococcus), isolation of patients with resistant respiratory tract infections, enteral nutrition (feeding through a tube), choice of gastrointestinal tract prophylaxis (antacid medication such as Magaldrate to prevent gastrointestinal bleeding) and subglottic secretion drainage (aspiration of secretions).

Pneumocystis Carinii /Pneumocystis Jiroveci Pneumonia (PCP)

Pneumocystis Carinii and Jiroveci are parasites which cause life threatening infections in the lungs. PCP was relatively uncommon until the 1980's when HIV virus emerged. The mode of transmission is unclear but it seems to represent the reactivation of a latent infection.

The onset of symptoms is usually gradual and may involve fever, cough and progressive dyspnea. Many patients are asymptomatic. The disease can present as a spontaneous pneumothorax (collapse of a lung due to air or gas in the cavity between the lungs and the chest wall).

The methods of diagnosing PCP include blood tests such as: CD4 also known as T cells count (used to check the health of the immune system), lactate dehydrogenase LDH (an enzyme present in almost all body tissues) and arterial blood gas ABG (also used to diagnose CAP). As HIV infection progresses, the number of CD4 cells declines. LDH is usually elevated in HIV patients and increasing levels despite the therapy correlates with poorer prognosis. If the ABG test reveals levels of the partial pressure of oxygen PaO2 less than 70 mmHg it is an indication that steroid treatment is needed.

Lung biopsy is a method of definitive diagnosis and it is dependant on the isolation of Pneumocystis agents from the sample. A biopsy is performed using a special needle or during surgery to remove tissue or cells from the lung for examination under the microscope.

The treatment for PCP includes: a combination of 2 antibiotics, antibacterial agents Trimethoprim and Sulfamethoxazole, Sulfones (Dapsone), Lincomycin antibiotics (Clindamycin), Antimalarials (Primaquine), Antiprotozoals (Atovaquone, Pentamidine).

The profilactic drugs usually prescribed for HIV patients to prevent PCP, also used for lungs infections like pneumonia, are: Trimethoprim/Sulfamethoxazole, Dapsone, Primethamine (Antiparasitic), aerosolized Pentamadine and Atovaquone (Antiprotozoal).