Pneumonia

Tx: Legionella or Mycoplasma

-A macrolide or a quinolone is the antibiotic of choice for pneumonias caused by either Legionella or Mycoplasma

viral pneumonia

-Although viruses are extremely common causes of upper respiratory tract infections, they are diagnosed relatively infrequently as a cause of frank pneumonia, except in children. -in adults the influenza virus is the most commonly diagnosed agent -outbreaks of pneumonia caused by adenovirus have also been described (particularly among military recruits)

Diagnosis of pneumonia

-As with other disorders affecting the pulmonary parenchyma, the single most useful tool for assessing pneumonia at the macroscopic level is the chest radiograph in both posteroanterior and lateral views. ~The radiograph not only confirms the presence of a pneumonia but also shows the distribution and extent of disease and sometimes give clues about the nature of the etiologic agent. -Chest radiographs also are useful for demonstrating the presence of pleural fluid, which frequently accompanies pneumonia, particularly of bacterial origin. ~The pleural fluid can be either thin and serous or thick and purulent; in the latter case, the term empyema is used -Microscopic examination of sputum may play an important role in evaluating patients with pneumonia. -pts. who require hospitalization, more of an effort is made to discover the offending agent -Routine stains and cultures of sputum are not useful for three of the important causes of pneumonia: Mycoplasma, Chlamydophila, and Legionella. ~Techniques for testing urine for the presence of antigens related to S. pneumoniae and Legionella are becoming increasingly useful. -PCR is now being widely used to detect Mycoplasma, chlmydophila and specific respiratory viruses such as influenza or coronaviruses -functional assessment of patients with acute infectious pneumonia is usually limited to evaluating gas exchange -ABG values characteristically demonstrate hypoxemia accompanied by normal or decreased PCO2, as well as widened A-a oxygen gradient -PFTs not very useful

Chlamydophila pneumoniae

-Chlamydophila pneumoniae has been recognized in epidemiologic studies as the cause of approximately 5% to 10% of cases of pneumonia. -It appears related to gram-negative bacteria, and for part of its life cycle it is an obligate intracellular parasite. -Diagnosis is rarely made clinically because of the lack of distinguishing clinical and radiographic features, and the organism is not readily cultured. -As a result, serologic studies serve as the primary means of diagnosis, although they are infrequently obtained and may be difficult to interpret.

Community acquired pneumonia

-Community-acquired pneumonia refers to pneumonia that develops in the community setting -this category is not meant to include patients with significant impairment of systemic host defense mechanisms, but it can include patients with other coexisting illnesses or risk factors that alter the profile of organisms likely to be responsible for pneumonia. -the cause of community-acquired pneumonia is never identified in a high proportion of patients, estimated to be up to 50%. -The likelihood of particular agents is believed to be influenced by a number of modifying factors: the presence of coexisting illness, recent treatment with antibiotics, residence in a nursing home, and the severity of illness at the initial presentation.

Tx: pneumococcal pneumonia

-For pneumococcal pneumonia, PCN has been the most appropriate agent traditionally, assuming the patient is not allergic -cases with various degrees of resistance to penicillin are encountered with increasing frequency. ~b/c penicillin is not effective against some of the other common causes of community-acquired pneumonia (Mycoplasma pneumoniae, C. pneumoniae), other classes of antibiotics with a broader spectrum against agents causing community-acquired pneumonia are typically used when antibiotics are initiated. -They include MACROLIDES (erythromycin or a derivative, such as azithromycin) and QUINOLONES (moxifloxacin). -When high-level resistance of pneumococcus to penicillin is found, either a quinolone or vancomycin is typically necessary. -Intermediately resistant strains can often be treated with ceftriaxone.

Tx: pneumonia due to H. influenzae

-H. influenzae may be sensitive to ampicillin -high frequency of organisms resistant to this antibiotic generally justifies alternative coverage, such as a second- or third-generation cephalosporin, an extended-spectrum macrolide, trimethoprim-sulfamethoxazole, a quinolone, or a β-lactam/β-lactamase inhibitor combination. -Many of the other gram-negative bacillary pneumonias often display resistance to a variety of antibiotics. ~Aminoglycosides (gentamicin and tobramycin), third- or fourth-generation cephalosporins, quinolones, carbapenems (e.g., meropenem), or an extended-spectrum penicillin with a β-lactamase inhibitor (e.g., piperacillin/tazobactam) may be used initially while antibiotic sensitivity testing is performed.

CXR IMAGE: Patch infiltrates

-Image is a patient with extensive gram-negative pneumonia -not patchy infiltrates throughout both lungs (more prominent on right) ~Staphylococcal and many of the gram-negative pneumonias may be localized or extensive and often follow a patchy distribution

AIDS and fungal infections

-In addition to Pneumocysti, several other fungi are recognized as causes of respiratory involvement in patients with AIDS, either as isolated respiratory system disease or as part of a disseminated infection. -The most common of these fungal infections is due to Cryptococcus neoformans, which more commonly causes meningitis than clinically apparent respiratory disease. ~Treatment traditionally has been with amphotericin B, but fluconazole has been used as an alternative agent. -Histoplasmosis and coccidioidomycosis are fungal infections that occur in specific endemic regions. ~In patients with AIDS, pulmonary involvement with these organisms is most commonly a manifestation of disseminated disease that resulted either from reactivation of previous disease or from progressive primary infection. -Tx: typically amphotericin B (or oral azole) is the primary agent used to treat either of these infections -other fungal infections are much less common in AIDS pts. (pulmonary infection w/ candida is extremely uncommon except at autopsy; aspergillus generally occurs in pts. with other predisposing factors for invasive aspergillosis, especially neutropenia)

Bronchopneumonia

-In bronchopneumonia, distal airway inflammation is prominent along with alveolar disease, and spread of the infection and the inflammatory process tends to occur through airways rather than through adjacent alveoli and acini. ~Whereas lobar pneumonias appear as dense consolidations involving part or all of a lobe, bronchopneumonias are more patchy in distribution, depending on where spread by airways has occurred. ~Many bacteria, such as staphylococci and a variety of gram-negative bacilli, may produce this patchy pattern.

Clinical features of pneumococcal pneumonia

-In pneumococcal pneumonia, the onset of the clinical illness often is relatively abrupt, with the sudden development of shaking chills and high fever. ~The cough may be productive of yellow, green, or blood-tinged (rusty-colored) sputum. ~Before the development of pneumonia, patients often have experienced a viral upper respiratory tract infection, which can be an important predisposing feature.

Interstitial Pneumonia

-Interstitial pneumonias are characterized by an inflammatory process within the interstitial walls rather than alveolar spaces. ~Although viral pneumonias classically start as interstitial pneumonias, severe cases generally show extension of the inflammatory process to alveolar spaces as well.

Lobar Pneumonia

-Lobar pneumonia has classically been described as a process not limited to segmental boundaries but rather tending to spread throughout an entire lobe of the lung. ~Spread of the infection is believed to occur from alveolus to alveolus and from acinus to acinus through interalveolar pores known as the pores of Kohn. ~The classic example of a lobar pneumonia is that due to S. pneumoniae, although many cases of pneumonia documented as being due to pneumococcus do not necessarily follow this typical pattern.

Myocobacterial infection and AIDS

-M. tuberculosis has emerged as an important respiratory pathogen in patients with AIDS, not only because it is common but also because it is potentially treatable. -Clinical disease may result from primary infection, reactivation of previous infection, or exogenous reinfection. -TB does not require a high degree of immunosuppression to produce disease and is often seen early in the course of disease in AIDS pts. -later in course of AIDS, upper lobe cavitary disease is less frequent and disseminated disease is more frequent than in pts. w/o AIDS -TB treatment in AIDS patients generally involves an expanded list of drugs given initially until the organism (plus sensitivity) is identified, treatment is also generally give for a longer duration -The other types of mycobacteria that frequently cause opportunistic infection in AIDS are members of the Mycobacterium avium complex (MAC). (typically associated with disseminated NOT pulmonary disease; prophylaxis should be considered when CD4 < 50)

Mycoplasma and pneumonia

-Mycoplasma appears to be a class of organisms that is intermediate between viruses and bacteria. ~Unlike bacteria, they have no rigid cell wall. ~Unlike viruses, they do not require the intracellular machinery of a host cell to replicate and are capable of free-living growth. ~Similar in size to large viruses, mycoplasmas are the smallest fully free-living organisms that have been identified thus far. -These organisms are now recognized as a common cause of pneumonia, and are perhaps responsible for a minimum of 10% to 20% of all cases. -Mycoplasmal pneumonia occurs most frequently in young adults but is not limited to this age group. -The pneumonia is generally acquired in the community -may occur in either isolated cases or localized outbreaks.

Clinical features of mycoplasmal pneumonia

-Mycoplasmal pneumonia, in contrast to pneumococcal pneumonia, characteristically has a somewhat slower, more insidious onset. ~Cough is a particularly prominent symptom, but it often is non-productive. ~Fever is not as high, and shaking chills are uncommon. ~Young adults are the individuals most likely to have mycoplasmal pneumonia, although the disease is not limited to this age group.

AIDS and Viral infection

-One of the most common viruses afflicting patients with AIDS is CMV, a member of the herpesvirus family -CMV most frequently involves eye and GI tract -occasionally CMV can be found in lung tissue of AIDS pts. -When patients with CMV in the lungs have clinical respiratory system disease, they almost always have a coexistent organism such as Pneumocystis that is thought to be the primary pathogen. -Other viruses such as herpes simplex, VZV, and EBV have been described as potential respiratory pathogens in AIDS, but they are distinctly uncommon

AIDS and bacterial infections

-Patients with AIDS appear to have an increased frequency of bacterial pneumonia, primarily due to either S. pneumoniae or H. influenzae. -The risk is increased at all levels of CD4+ count and is highest when the count falls below 200 cells/mm3 . -IV drug users appear to be at particularly high risk. -Bacterial pneumonias might not be predicted as a complication of AIDS, because impairment in cellular immunity should not by itself predispose an individual to these infections. ~dysregulation of the humoral immune system accompanies the impairment in cellular immunity. ~Patients frequently have polyclonal hyperglobulinemia at the same time they demonstrate a poor antibody response after antigen exposure. ~Presumably, loss of helper-inducer cells results in alteration of the normal interaction between helper-inducer cells and B lymphocytes that regulates antibody production.

Clinical features of staph/gram negative bacillary pneumonias

-Patients with either staphylococcal or gram-negative bacillary pneumonias are often quite ill. ~Frequently these patients have complex underlying medical problems and have already been hospitalized. ~Many have impaired defense mechanisms or have recently received antibiotics. ~Staphylococcal pneumonia classically may be seen as a secondary complication of influenza infection or as a result of dissemination of the organism through the bloodstream

PE findings in pneumonia

-Physical examination reflects the systemic response to infection and the ongoing inflammatory process in the lung. ~Patients often have tachycardia, tachypnea, and fever. ~Examination of the chest typically reveals crackles or rales overlying the region of the pneumonia (If dense consolidation is present and the bronchus supplying the area is patent, sound transmission is greatly increased through the consolidated pneumonic area) -As a result, breath sounds may be increased and bronchial in quality, fremitus is increased, and egophony is present. ~The consolidated area is characteristically dull to percussion of the overlying chest wall. ~Examination of peripheral blood generally shows an increase in white blood cell count (leukocytosis). -Especially in patients with bacterial pneumonia, the leukocytosis is composed primarily of PMNs, and a shift toward greater numbers of immature neutrophils such as band forms may be seen.

Clinical features of Legionnaire's disease

-Pneumonia caused by L. pneumophila, commonly called Legionnaires' disease , can be seen as isolated cases or localized outbreaks. ~Otherwise healthy hosts may be affected, but patients with impaired respiratory defense mechanisms appear to be predisposed. ~Patients are often extremely ill, not only with respiratory compromise and even respiratory failure but also with nonrespiratory manifestations; specifically, gastrointestinal, central nervous system, hepatic, and renal abnormalities may accompany the pneumonia.

Tx: pneumonia due to anaerobes

-Pneumonia caused by anaerobes is treated most commonly with either penicillin or clindamycin.

Clinical features of pneumonia with anaerobic organisms

-Pneumonia with anaerobic organisms generally occurs in patients with impaired consciousness or difficulty swallowing who cannot adequately protect the airway from aspiration of oropharyngeal secretions. ~Dentition often is poor, and patients frequently have gingivitis or periodontal abscesses. ~Clinical onset of the pneumonia tends to be gradual, and sputum may have a particularly foul odor, suggesting anaerobic infection. ~Successful culture of causative organisms may be difficult. ~While generally slow growing, anaerobic organisms can cause substantial tissue destruction, and necrosis of affected tissue and abscess formation are relatively common sequelae.

Tx: pneumonia caused by staphylococci

-Staphylococci generally produce penicillinase, which requires the use of a penicillinase-resistant semisynthetic derivative of penicillin, such as oxacillin or nafcillin. ~Many staphylococci are also resistant to these derivatives, in which case vancomycin is the antibiotic of choice.

Tx: bacterial pneumonia

-The cornerstone of treatment of bacterial pneumonia is prompt, effective, antibiotic therapy directed at the infecting organism. ~b/c the causative organism often is not known when the pneumonia is first diagnosed and, in fact, frequently is not identified at any point during the clinical course, initial treatment strategies have been developed on the basis of the clinical setting (community-acquired vs. hospital-acquired pneumonia). ~If and when an organism is identified, the regimen may be changed to allow for more focused or more effective antibiotic coverage.

Pathophysiology of pneumonia

-The major pathophysiologic consequence of inflammation and infection involving the distal air spaces is decreased ventilation to affected areas. ~If perfusion is relatively maintained, as it often is because of the vasodilatory effects of inflammatory mediators, ventilation-perfusion mismatch results, with low ventilation-perfusion ratios in diseased regions. ~When alveoli are totally filled with inflammatory exudate, there may be no ventilation to these regions, and extreme ventilation-perfusion inequality (shunt) results. ~Ventilation-perfusion inequality generally manifests as hypoxemia. ~Although shunt may explain part of the hypoxemia, ventilation-perfusion mismatch with areas of low ventilation-perfusion ratio is usually a more important factor. -CO2 retention is not a feature of pneumonia unless the patient already has an extremely limited reserve, especially from underlying COPD. ~In fact, patients with pneumonia frequently hyperventilate and have a Pco2 less than 40 mm Hg.

Pneumonia pathology

-The pathologic process common to all pneumonias is infection and inflammation of the distal pulmonary parenchyma. -An influx of polymorphonuclear leukocytes (PMNs), edema fluid, erythrocytes, mononuclear cells, and fibrin develops to a variable extent in all cases -Bacterial pneumonias in particular are characterized by an exuberant outpouring of PMNs into alveolar spaces as they attempt to limit proliferation of the invading bacteria. -Individual types of pneumonia may differ in exact location and mode of spread of the infection.

Systemic response to pneumonia

-The systemic response to pneumonia is not unique but rather is a reflection of the body's response to serious infection. ~Perhaps the most apparent aspects of this response are fever, an outpouring of PMNs into the circulation (particularly with bacterial pneumonia), and often a "toxic" appearance of the patient. ~These indirect systemic responses can be clues that an infectious process is the cause of a new pulmonary infiltrate.

Empyema

-The term empyema (or more properly, empyema thoracis) refers to pus in the pleural space. ~In its most florid form, an empyema represents thick, creamy, or yellow fluid within the pleural space. ~The fluid contains enormous numbers of leukocytes, primarily PMNs, often accompanied by bacterial organisms. ~With a true empyema or often even with other grossly inflammatory pleural effusions accompanying pneumonia (parapneumonic effusions), pleural inflammation can result in formation of localized pockets of fluid or substantial scarring and limited mobility of the underlying lung. -Several different bacterial organisms may be associated with development of an empyema. ~Anaerobes are particularly common, but staphylococci and other aerobic organisms are also potential causes. -After an empyema has been documented, usually by thoracentesis and sampling of pleural fluid, drainage of the fluid is required. -In many cases thoracoscopic surgery is performed to completely drain the pleural space. -Alternative techniques are used in some specific clinical situations and can include open surgical procedures or placement of large-bore chest tubes with repeated instillation of fibrinolytic agents (alteplase and DNase) into the pleural space.

Initial pneumonia evaluation/treatment -patient category (community-acquired pneumonia): Hospitalized, severe pneumonia

-The third group is defined by a need for hospitalization. -The fourth group includes patients with the most severe disease, which necessitates admission to an intensive care unit (ICU). -Antibiotics, such as a quinolone or an advanced-generation macrolide, plus a β-lactam (particularly a third-generation cephalosporin), a carbapenem, or an extended-spectrum penicillin with β-lactamase inhibitor, are typically used in these settings, frequently in combination with vancomycin. -Common organisms: S. pneumoniae; H. influenzae; polymicrobial (including anaerobes); aerobic gram-negative baccili; Legionella; C. pneumoniae; -Other miscellaneous organisms: M. catarrhalis; Legionella; M. tuberculosis; Endemic fungi -initial treatment: IV Beta-lactam plus IV or oral macrolide or doxycycline OR IV quinolone

Streptococcus pneumoniae

-a normal inhabitant of the oropharynx in a large proportion of adults -Gram-positive coccus (typically diplococci) ~Pneumococcal pneumonia is commonly acquired in the community and frequently occurs following a viral upper respiratory tract infection. ~The organism has a polysaccharide capsule that interferes with immune recognition and phagocytosis, and therefore is an important factor in its virulence. -There are many different antigenic types of capsular polysaccharide, and for host defense cells to phagocytize the organism, the antibody against the particular capsular type must be present. -Antibodies contributing in this way to the phagocytic process are called opsonins

Klebsiella pneumoniae

-a relatively large gram-negative rod normally found in the gastrointestinal tract -has been best described as a cause of pneumonia in the setting of underlying alcoholism.

Haemophilus influenzae

-a small coccobacillary gram-negative organism, is often found in the nasopharynx of normal individuals and in the lower airways of patients with COPD. -It can cause pneumonia in children and adults —in adults often with underlying COPD as a predisposing factor.

Lung abscess as a complication of pneumonia

-abscess= local collection of pus -lung abscesses generally result from tissue destruction complicating a pneumonia. -The abscess contents are primarily PMNs, often with collections of bacterial organisms. -after antibiotics, organisms may no longer be culturable from the abscess cavity. -Etiologic agents associated with formation of a lung abscess are generally those bacteria that cause significant tissue necrosis. ~Most commonly, anaerobic organisms are responsible (aspiration of oropharyngeal contents is likely the predisposing event) ~aerobic organisms, such as Staphylococcus or enteric gram-negative rods, can also cause significant tissue destruction with cavitation of a region of lung parenchyma and abscess formation. -Treatment of a lung abscess involves antibiotic therapy, often given for longer than for an uncomplicated pneumonia. -Although abscesses elsewhere in the body are drained by surgical incision, lung abscesses generally drain through the tracheobronchial tree, and surgical intervention or placement of a drainage catheter is needed only rarely.

noscomial (hospital-aquired pneumonia)

-acquired pneumonia, noscomial pneumonia is acquired by hospitalized patients, generally after more than 48 hours of hospitalization -Patients in ICUs, especially those receiving mechanical ventilation, are at particularly high risk for developing this category of pneumonia. -atypical colonization of the oropharynx by organisms not usually present followed by microaspiration of oropharyngeal secretions into the tracheaobronchial tree is the most common problem leading to noscomial pneumonia -Patients at risk often have other underlying medical problems, have been receiving antibiotics, or have an endotracheal tube in their airway that bypasses some of the normal protective mechanisms of the respiratory tract. -gastric acid reducing medications (PPIs) may increase the risk for noscomial pneumonia -Organisms of particular concern in patients who develop hospital-acquired pneumonia are enteric gram-negative bacilli and S. aureus, but other organisms such as Pseudomonas aeruginosa and Legionella can be involved.

Immune reconstruction inflammatory syndrome

-for patients with AIDS and tuberculosis (or with other opportunistic infections), improvement in the patient's overall immune status can be associated with a paradoxical clinical worsening of symptoms from the opportunistic infection. ~In these cases, "reconstitution" of the immune system results in an augmented inflammatory reaction to the opportunistic infection, leading to the apparent clinical worsening known as immune reconstitution inflammatory syndrome

Pseudomonas aeruginosa

-found in a variety of environmental sources (including the hospital environment), is seen primarily in patients who are debilitated, hospitalized, and often previously treated with antibiotics. -P. aeruginosa is also a very common cause of respiratory tract infections in patients with underlying bronchiectasis or cystic fibrosis.

Staphylococcus aureus

-gram-positive coccus, but usually appears in clusters when examined microscopically. ~Three major settings in which this organism is seen as a cause of pneumonia are (1) as a secondary complication of respiratory tract infection with the influenza virus (2) in the hospitalized patient, who often has some impairment of host defense mechanisms and whose oropharynx has been colonized by Staphylococcus (3) as a complication of widespread dissemination of staphylococcal organisms through the bloodstream.

Legionella pneumophila

-important cause of pneumonia occurring in epidemics as well as in isolated sporadic cases -seems to affect previously healthy individuals and those with prior impairment of respiratory defense mechanisms -retrospectively, several prior outbreaks of unexplained pneumonia have been shown to be due to legionella -although the organism is a gram-negative bacillus, it is poorly visualized by conventional staining methods

Most frequent causes of pneumonia

-largest single category of agents is probably bacteria -the other categories are viruses and mycoplasma -of the bacteria streptococcus pneumonia (pneumococcus) is the most frequently associated with pneumonia -estimated that 1/2 of all pneumonias in adults requiring hospitalization are caused by S. pneumoniae

Intrathoracic complications of pneumonia

-lung abscesses and empyema

Tx: viral pneumonia

-no definitive treatment -influenza vaccine is effective prevention in majority of individuals who receive it -antiviral agents may reduce severity of illness if give soon after the onset of clinical symptoms -other therapy is mainly supportive (Chest physical therapy to assist in clearance of respiratory secretions; supplemental O2)

General Clinical features of pneumonia

-the clinical manifestations of pneumonia share many similarities and differences ~in many cases of pneumonia a specific agent cannot be clearly identified, and patients often are managed in an empirical way based on the setting in which they present. -Perhaps the most important constellation of symptoms in almost any type of pneumonia consists of fever, cough, and often shortness of breath -cough can be either productive (usually bacterial) or nonproductive (usually viral or mycoplasma) -patients often report pleural chest pain

How do microorganisms enter the respiratory tract?

1. inhalation -microbes usually carried in small droplet particles inhaled into the tracheobronchial tree. 2. aspiration -secretions from the oropharynx pass through the larynx and into the tracheobronchial tree. -clinically significant aspiration is more likely to occur in individuals unable to protect their airways from secretions by glottic closure and coughing -everyone is subject to aspirating small amounts of oropharyngeal secretions, particularly during sleep -defense mechanisms seem able to cope with nightly attack of bacteria 3. less commonly bacteria reach pulmonary parenchyma through the blood stream -certain organisms (particularly staph) are spread this way -usually when bacteremia is present, the bacteria is introduced by a distant primary bacterial infection

Bacterial flora of the mouth and pneumonia (anaerobic pneumonia)

~A multitude of organisms (both gram-positive and gram-negative) that favor or require anaerobic conditions for growth are the major organisms comprising mouth flora. ~The most common predisposing factor for anaerobic pneumonia is the aspiration of secretions from the oropharynx into the tracheobronchial tree. ~Patients with impaired consciousness and those with difficulty swallowing are prone to aspirate and are at greatest risk for pneumonia caused by anaerobic or mixed mouth organisms. ~In addition, patients with poor dentition or gum disease are more likely to develop aspiration pneumonia because of the larger burden of organisms in their oral cavity. ~In some settings, such as prolonged hospitalization or recent use of antibiotics, the type of bacteria residing in the oropharynx may change. -Specifically, aerobic gram-negative bacilli and S. aureus are more likely to colonize the oropharynx, and any subsequent pneumonia resulting from aspiration of oropharyngeal contents may include these aerobic organisms as part of the process.

Microscopic sputum examination in pneumonia

~In most bacterial pneumonias, large numbers of PMNs are seen in the sputum. ~In contrast, mycoplasmal and viral pneumonias have fewer PMNs and more mononuclear inflammatory cells. ~Pneumococcal, staphylococcal, and gram-negative bacillary pneumonias commonly demonstrate a relatively homogeneous population of the infecting bacteria. ~Anaerobic aspiration pneumonias, caused by a mixture of organisms from the oropharynx, show a mixed population of bacteria of many different morphologies. ~In Legionnaires' disease, the bacterium does not stain well with the usual Gram stain reagent and generally requires special stains to appreciate its presence. ~In mycoplasmal and viral pneumonia, the infecting agent is not visualized by light microscopy, and only the predominantly mononuclear cell inflammatory response is seen -gram stain and cultures are used but some bacteria are difficult to grow

Pneumocystis jiroveci Pneumonia

~In patients with AIDS, onset of the disease is often more indolent than in immunosuppressed patients without AIDS. ~Fever, cough, and dyspnea are the usual symptoms -CXR shows diffuse interstitial or alveolar infiltrates. ~Often the lung fields look hazy, a pattern that may be difficult to characterize specifically as either interstitial or alveolar and commonly described as looking like "ground glass". -Diagnosis is generally based on finding the organism in respiratory secretions (pts. w/AIDS typically have a large burden of organisms) -Treatment of severe pneumonia caused by Pneumocystis organisms usually involves one of the following regimens: the combination antimicrobial trimethoprim-sulfamethoxazole (which is preferred if tolerated), the combination of clindamycin and primaquine, the combination of trimethoprim and dapsone, or pentamidine as a single agent given intravenously. -NOTE: pts. with AIDS tend to have a predisposition to allergic reactions w/sulfonamides -In patients with moderate to severe disease caused by Pneumocystis pneumonia, adjunctive therapy with corticosteroids is helpful in averting respiratory failure. -In patients with AIDS, oral administration of trimethoprim-sulfamethoxazole (in low doses) or dapsone (either alone or with pyrimethamine) can be used with reasonable effectiveness to prevent Pneumocystis pneumonia. (prophylactic treatment is recommended when CD4 count < 200) ~When Pneumocystis pneumonia develops despite use of aerosolized pentamidine prophylaxis, the clinical presentation may be atypical.

Radiographic findings in Legionella pneumonia

~Legionella pneumonia most commonly presents with a patchy or consolidated unilobar infiltrate, although all patterns have been described.

Radiographic presentations of mycoplasma pneumonias

~Mycoplasma organisms can produce a variety of radiographic presentations, which are classically described as being more impressive than the clinical picture would suggest

CXR IMAGE: aspiration pneumonia

~Pneumonias caused by aspiration of oropharyngeal secretions characteristically involve the dependent regions of lung: the lower lobe in the upright patient or the posterior segment of the upper lobe or superior segment of the lower lobe in the supine patient

CXR IMAGE: lobar pneumonia

~The classic pattern for S. pneumoniae (pneumococcus) and K. pneumoniae is a lobar pneumonia

Initial pneumonia evaluation/treatment -patient category (community-acquired pneumonia): outpatient, w/o cardio-pulmonary disease or other modifying risk factors

~The first group comprises patients who do not have coexisting cardiopulmonary disease or other modifying risk factors, who have not used antibiotics in the previous 3 months, and who do not require hospitalization. -Common organisms: S. pneumoniae; M. pneumoniae; C. pneumoniae; respiratory viruses; H. infulenzae (smokers) -Other Miscellaneous organisms: legionella; M. tuberculosis; endemic fungi -initial therapy: advanced generation macrolide (azithromycin or clarithromycin) OR doxycycline

Initial pneumonia evaluation/treatment -patient category (community-acquired pneumonia): outpatient w/cardiopulmonary disease and/or other modifying risk factors

~The second group includes patients who have coexisting cardiopulmonary disease or other modifying risk factors but still can be treated in an outpatient setting. -Important comorbidities that place a patient in this category include chronic heart, lung, hepatic, or renal disease; DM; alcoholism; malignancies; asplenia; immunosuppressive conditions or drugs; or the use of antibiotics within the prior 3 months (in which case, antibiotics from a different class should be used) -Common organisms: S. pneumoniae; M. pneumoniae; H. influenzae; aerobic gram-negative baccili; respiratory viruses; anaerobes; C. pneumoniae -Other miscellaneous organisms: M. catarrhalis; Legionella; M. tuberculosis; Endemic fungi -Initial therapy: oral quinolone (w/activity against pneumococcus) OR beta-lactamase plus macrolide

Factors leading to impairment of host defenses contributing to the development of pneumonia

~Viral upper respiratory tract infections -ethanol abuse -cigarette smoking -heart failure -preexisting chronic obstructive pulmonary disease (COPD) -these impairments can occur in patients not considered immunosuppressed -more severe impairment of host defenses is caused by diseases associated w/immunosuppression: AIDS, various underlying malignancies, use of corticosteroids and other immunosuppressive drugs ~In these cases associated with impairment of host defenses, individuals are susceptible to both bacterial and more unusual nonbacterial infections