see also Streptococcus pneumoniae
Introduction:
Pneumonia is common across all age groups but it is a leading cause of death among the old and immunosupressed. There are two broad classifications, community acquired pneumonia (CAP) and hospital acquired pneumoniae (HAP).
Pneumonia can be caused by the flu, COVID-19 or many other infectious agents. Bacteria, fungi and a wide variety of virsues can cause pneumonias and there is a lot of variation in the virulence of different pathogenic agents. Health providers make a distinction between viral pneumonia and bacterial pneumonia. Viral pneumonia follows on from a cold or flue that persists. Bacterial pneumonia is caused by bacteria and may be accompanied by a mucus-y cough, high fever and severe chest paints.
Community acquired pneumonia (CAP):
CAP is infectious pneumonia in a person who has not been recently hospitalized. It is the most common type of pneumonia.
Gram positive bacteria causes include Streptococcus pneumoniae and staphylococcus aureus.
Gram negative bacteria causes include Haemophilus influenza, Klebsiella pneumonia, Escherichia coli, Pseudomonas aeruginosa, and Moraxella catarrhalis. These bacteria often live in the stomach or intestines and may enter the lungs if vomit is inhaled.
Atypical bacterial causes include Chlamydophila pneumoniae, Mycoplasma pneumonia (also called “walking pneumonia which is less severe), and Legionella pneumophila.
Viral causes include influenza, respiratory syncytial virus (RSV), adenovirus, and parainfluenza. Viruses account for about 20% of pneumonia according to some studies. SARS-CoV-2 was recognized as causing a deadly pneumonia. Hantavirus which appared in the US in 1993 and was associated with mice is an enveloped virus of the Bunyaviridae family which is transmitted via airborne dust contaminated with the feces or saliva of infected rodents. Hantavirus had peviously only been known to casue severe kidney disease and hemorrhagic fevers in other parts of the wrold. the new condition was named hantavirus pulmonary syndrome (HPS).
Fungus causes include histoplasma capsualtum which appears to grow most abundantly in moist soils high in nitrogen content, especially those supplemented by bird and bat droppings. Although the fungus Pneumocystis jivovecil (formerly called P. carinii) was discovered in 1909, it remained relatively obscure until it was suddenly propelled into clinical prominence as the agent of Pneumocystis pneumonia. PCP is one of the most fequent opportunistic infections in AIDS pateints. Cancer patietns adn others with extreme immunosuppression are also at risk for this disease.
–Pneumocystis carinii pneumonia (PCP), now referred to as Pneumocystis jirovecii pneumonia, is a fungal infection that most commonly affects the immunocompromised and, in some cases, can be severely life-threatening. Typically, patients at risk are those with underlying disease states that alter host immunity, such as cancer, human immunodeficiency virus, transplant recipients, or those taking immunosuppressive therapies and medications. Patients presenting with PCP may show signs of fever, cough, dyspnea, and, in severe cases, respiratory failure.
Pneumocystis is thought to be transmitted from person to person through an airborne route.
Asymptomatic lung colonization can occur in people with normal immune systems, and they
may unknowingly become reservoirs (asymptomatic carriers) for the spread of Pneumocystis to
immunocompromised individuals.
Hospital acquired pneumoniae (HAP):
HAP also called nosocomial pneumonia is acquired during or after hospitalization for another illness or procedure with an onset 72 hours after admission. Up to 1% of hospitalized people experience the complication of pneumonia. Together with surgical site infections, it is the most common healthcare associated infections. It is most comonly associated with mechanical ventilation, via an endotracheal or tracheostomy tube. Sometimes it is labeled “ventilator associated pneumonia” or VAP. The mortality rate is quite high –between 30-50%.
The most frequent cause of all forms of healthcare associated pneumonia are MRSA strains of Staphylococcus aureus. After MRSA, gram negative bacteria are most common. These include Klebsiella pneumoniae, Enterobacter, E. coli, Pseudomonas aeruginos and Acinetobacter. Some of these strains are highly antibiotic resistant. When they are resistant ot a last line antibotic (carbapenem) there are designated as an urgent threat by the CDC.
Hospital acquired microorganisms can include resistant bacteria such as , Pseudomonas, Enterobacter, and Serratia. Because individuals with HAP are immunosuppressed to start with, this type of infection is typically more deadly then CAP. Nationwide, about 6% of hospitals have problems with “superbugs” known as carbapenem-resistant bacteria such as Klebsiella pneumonia. For example, the NIH in 2011 had such an outbreak which killed 11 of their patients. 6 of the patients had immune systems weakened by cancer and drugs given after organ transplants.
Symptoms: Pneumonia is an inflammatory condition of the lung which is often is characterized by air sacs (alveoli) filling with fluid. Symptoms of pneumonia include cough, chest pain, fever, and difficulty breathing. Other symptoms include coughing up blood, blueness of the skin, nausea, vomiting, and joint pains.
Diagnosis: Cultures of sputum of tracheal swabs is not very useful in daignosing health car associated pneumonia because the condition is usually caused by normal biota. Cultures of fluids obtained through endotracheal tubes or from bronchalveolar lavage provide better information but are fairly intrusive. It is also important ot recall that if the patient has already received antibiotic, culture resutls will be affected.
Prevention: Because most healthcare associated pneumonias are caused by microorganisms aspirated form the upper respiratory tract, measures that discourage the transfer of microbe into the lungs are useful for preventing the condition. Elevating patients’ ehads to a 30 to 45 degree angle helps reduce aspiration of secretions. Deep breathing and frequent coughing can reduce postoperative infection rates. Proper care of mechanical ventilation and respiratory therapy equipment is essential.
Treatment: studies have shown that delaying antibiotic treatment of suspected healthcare associated pneumonia leads to a greater likelihood of death. Even in the era of conservative antibiotic use, empiric therapy should be started as soon as healthcare associated pneumonia is suspected, using multiple antibiotic that cover both gram negative and gram positive organisms.
Klebsiella:
Klebsiella species cause a wide range of diseases including pneumonia, urinary tract infections (UTIs), bloodstream infections and sepsis. These infections are particularly a problem among neonates, elderly and immunocompromised individuals. Klebsiella is also responsible for a significant number of community-acquired infections. A defining feature of these infections is their morbidity and mortality, and the Klebsiellastrains associated with them are considered hypervirulent. lebsiella species are ubiquitously found in nature including water, soil and animals, and they can colonise medical devices and the healthcare environment See Pessoa
Klebsiella pneumonia is a type of Gram-negative bacteria that can cause different types of healthcare-associated infections, including pneumonia, bloodstream infections, wound or surgical site infections, and meningitis. Increasingly, Klebsiella bacteria have developed antimicrobial resistance. See CDC
Klebsiella pneumoniae causes suppurative infections, bacteriemia, and septicemia and also accounts for a substantial percetnage of nosocomial infections in noenates. Mortality rates reported for K. pneumoniae bacteremia range from 20-50%.
–Virulence Factors:
—-Capsule: The capsular polysaccharide and type 1 fimbriae are two of the major surface-located virulence properties associated with the pathogenesis of Klebsiella pneumoniae. The capsule is an elaborate polysaccharide matrix that encases the entire cell surface and provides resistance against many host defense mechanisms. See Klemm
Research on the pathogenesis of experimental infections with K. pneumoniae has shown the capsular polysacccharide (CPS) to be a prime factor in virulence. The majority of clinically isolated K. pneumoniae strains have a well definced capsule. Almost all clinical isolates of K. pneumoniae are encapsulated and at least 77 chemically and antigenically distinct CPS types have been recognized. Certain CPS types can promote the binding of K. pneumoniae to guinea pig alveolar macrophages and that this binding is followed by ingestion and killing of the bacteria. The molecular basis for this type of phagocytosis, termed lectinophagocytosis, invovles macrophage mannose receptor. This macrophage receptor reognizes sequences such as Man-alpha2/3-Man and Rha-alpha2/3-Rha found in the CPS of a number of capsular sertoypes. Thus the capsule type plays an important role in the rate of blood clearance and phagocytosis. (Kabha, “Relationships among Capsular Strcuture, phagocytosis and mouse virulene in Klebsiella pneumoniae” Infection & Immunity, 1995)
Carbapenem-resistant (CR) Klebsiella pneumoniae has emerged as an urgent public health threat in many industrialized countries worldwide, including the United States. Infections caused by CR K. pneumoniae are difficult to treat because these organisms are typically resistant to multiple antibiotics, and the patients have significant comorbidities. Notably, there is high (∼50%) mortality among individuals with bacteremia caused by CR K. pneumoniae. See Deleo
Treatment:
Symptoms of pneumonia needs immediate medical attention. Treatment includes antibiotics. If a patient’s condition does not improve or if there is doubt about the diagnosis, a culture of the sputum may be tested.
Many people with pneumonia need antibiotics even if an infectio had a viral origin becasue a bacterial infection may have set in.
A vaccine against Streptococcus pneumoniae is available and is recommended for all adults over 65. A repeat vaccine may be required after 5- 10 years. Influenza vaccines should be given at the same time.
Complications:
Ventilator-associated pneumonia (VAP): is a frequent complication in patients requiring mechanical ventilation with an incidence rate of 10-25% and a crude mortality ranging from 10% to 40%. M