LOWER RESPIRATORY TRACT INFECTIONS By Dr Izhar

Acute bronchitis

Acute bronchitis is common in smokers and in patientswith asthma, chronic bronchitis and emphysema. However,it also occurs in otherwise healthy individuals, usually dueto viral infections. In both groups, when bacterial infectionoccurs, the bacteria most often incriminated are Strep,pneumoniae or H. influenzae.

These infections cause anacute inflammation of the trachea and major airways, andas a consequence of this there is chest pain, commonlyexperienced as a raw feeling maximal on deep inspiration,as well as chest tightness. The patient may wheeze. Inpatients with pre-existing chronic airflow limitation thedevelopment of acute bronchitis can cause severe breathlessness.

Acute bronchitis causes an irritating, persistentdry cough, although after 1 or 2 days patients producesmall amounts of mucoid thick sputum which subsequentlybecomes more plentiful and purulent. Appropriate antibiotictherapy is amoxycillin, erythromycin or tetracycline. Inpatients with chronic airflow limitation, aggressive therapywith bronchodilators is important, as acute bronchitis canprecipitate a worsening of respiratory failure.

PNEUMONIA

Pneumonia remains an important clinical problem, causingmany more deaths than any other infectious disease in theUK, both in the community and in hospitals. In recentyears the aetiology of the pneumonias has changed with,for example, an increased incidence of opportunisticpneumonias in the immunocompromised host, particularlypatients with HIV infection.

Pneumococcal pneumonia

Pneumococcal pneumonia is more common in the wintermonths and upper respiratory tract viral infections are apredisposing factor. Fever is often high and there may berigors. Pleurisy is common and the cough, which is initiallydry and painful, subsequently becomes productive of rusty sputum. Altered blood from the congested lung tissue gives the sputum its characteristic colour. Labial herpes simplexis common (30% of cases). In some cases the onset ofsymptoms in pneumococcal pneumonia can be very rapidand patients may be critically ill within a few hours. In theusual case clinical examination demonstrates cracklesmore than classic signs of consolidation, and a pleural rubis common. The chest X-ray shows hazy shadowing, oftenwith an air bronchogram, in any lobe, although lower lobesare the most frequently involved. In the majority of casesthe consolidation does not involve the whole lobe.

Mildly or moderately ill patients can be managed adequatelyat home and are satisfactorily treated with oralamoxycillin or erythromycin. Severely ill patients shouldbe transferred to hospital for the adequate treatment ofpain, dehydration and hypoxaemia. A Gram stain of thesputum will show typical Gram-positive diplococci, andblood cultures will be positive in 25-40% of untreatedcases. If the specific diagnosis is established, benzylpenicillinis the treatment of choice, but patients also do wellwith amoxycillin.

Recovery from pneumococcal pneumonia is usuallyrapid, although the X-ray may take several weeks to returnto normal, as is the case with most pneumonias. In patientswho are more severely ill and who are bacteraemic, mortalitymay be as high as 25%. Of all pneumonias, pleuraleffusion is most common in association with pneumococcalinfection. Empyema complicating the pleural effusionis now relatively rare and occurs in 3% of cases with positiveblood cultures. In such blood culture-positive patientspneumococcal pneumonia can be complicated by pericarditis,endocarditis, septic arthritis, peritonitis, cellulitis and, on rare occasions, meningitis.

Haemophilus influenzae pneumoniaIt is unusual for H. influenzae to cause pneumonia inpreviously fit individuals. However, it is probably the mostcommon cause of infection in patients with pre-existinglung disease, particularly in those with chronic bronchitisand emphysema. It is the organism most often responsiblefor the exacerbations that occur in chronic bronchitis,sometimes complicating an initial viral infection. The chestX-ray distinguishes haemophilus bronchopneumonia fromsimple infective bronchitis by showing shadowing, usuallyas nodules 0.5-3.0 cm in diameter at both bases, and onexamination there may be bronchial breathing. The samepicture of bronchopneumonia is sometimes seen withstaphylococcal and pneumococcal infection.

Bronchopneumonia is very common. Patients are oftenwheezy and progressively more breathless. There is usuallyfever, but in elderly and debilitated patients the temperaturecan be normal. Cough and purulent sputum areprominent features. As a consequence of diffuse airwayinflammation and intraluminal sputum, patients withchronic bronchitis are frequently precipitated into respiratoryfailure and cor pulmonale. The first-line treatmentof H. influenzae bronchopneumonia is intravenouscefuroxime unless the isolate is known to be sensitive toamoxycillin.

Staphylococcal pneumonia

Staphylococcal infection causes more necrosis than otherorganisms responsible for pneumonia, and there is a highincidence of abscess formation. In the community staphylococcalpneumonia is not common (about 1% of cases),but it is an important and serious complication of influenzaand is therefore more common during influenza epidemicsand during the winter months. Staphylococcal lobar pneumoniacan be fulminant and rapidly fatal.

In most casesthe clinical picture is similar to that of pneumococcalpneumonia, but haemoptysis is more common. Cavitationis unusual in community-acquired pneumonias, withthe exception of staphylococcal or particularly virulentserotype 3 pneumococcal infections. The chest X-raytypically shows bilateral consolidation, usually basal, withabscesses that are thin-walled and cyst-like. Staphylococcallung abscesses may rupture into the pleural cavity, resultingin pneumothorax or pyopneumothorax.

In the community, the development of pneumonia asa complication of influenza should be treated with flucloxacillinin addition to amoxycillin. Following admissionto hospital, a Gram stain of the sputum is helpful in confirmingthe diagnosis and blood cultures are frequentlypositive. With a definite diagnosis treatment should bewith intravenous flucloxacillin (l-2gqds) and fusidic acid.Although the majority of patients make a good recoveryfrom staphylococcal pneumonia, the combination ofinfluenza A infection and staphylococcal pneumonia stillcarries an appreciable mortality. Important complicationsinclude the haematogenous spread of infection to brain,bone and other organs, and occasionally patients candevelop acute bacterial endocarditis.

Legionella pneumonia

Legionella pneumonia was first recognized in 1976 afteran outbreak of pneumonia with a high mortality at aLegionnaires’ conference in Philadelphia. The pathogen isnow known as Legionella pneumophila, a small Gramnegativecoccobacillary organism. Infection is acquiredfrom contaminated water, usually in air-conditioningsystems and showers in hotels and hospitals, and transmissiondoes not occur from person to person.

Most cases havebeen in middle-aged or elderly males and have occurred inthe summer months. Legionella is a cause of opportunisticchest infection in immunocompromised patients. Clinically,legionella pneumonia resembles viral or mycoplasmainfection. There is a cough but little sputum, which ismucoid, not purulent. Patients are frequently severely ill,with high fever, rigors, confusion, myalgia, abdominalpain, vomiting and diarrhoea. Hyponatraemia, hypoalbuminaemiaand haematuria (50% of cases) are common.The white cell count may be normal or modestly elevated,but is seldom above 15000 x 106/L. Gram stain of themucoid sputum reveals no organisms. The chest X-ray mostcommonly shows patchy shadowing, which can be bilateraland which progresses to lobar consolidation.

The diagnosis is usually retrospective and based on agreater than fourfold increase in the indirect fluorescentantibody titre. Legionella antigen can be detected in theurine, and this has proved to be a more useful test inthe acute setting. The organism can be isolated fromlung tissue, pleural fluid and blood. Treatment is witherythromycin (1 g 6-hourly) for a period of 3 weeks or clarithromycin(SOOmgbd). If the diagnosis is strongly suspected,or confirmed, and particularly in patients who failto respond, or who are severely ill, rifampicin should beadded. Ciprofloxacin may also be effective. The overallmortality is 15%, some patients dying despite appropriateantibiotic therapy.

Viral and viral-like pneumonia

Viral and viral-like pneumonias  are characterizedby fever, systemic symptoms (e.g. myalgia,headache) and a normal or near-normal white cell count.Respiratory syncytial virus infection is important in children.Influenza and measles are frequently complicated byserious bacterial infection, particularly staphylococcal.Cytomegalovirus is a cause of pneumonia in the immuno compromised host. Of the remaining causes,Mycoplasma pneumoniae, Chlamydia psittaci and Coxiellaburnetii are the most important.

Mycoplasma pneumonia

M. pneumoniae is the most important agent causing the socalled’atypical’ pneumonias. In the past, this organism wasthe cause of major outbreaks of pneumonias in the armedforces; many cases still occur in clusters, and epidemicstypically occur every 3 or 4 years. Infection is caused by anorganism of the mycoplasma group, the smallest knownfree-living organism. Most patients are aged between 15and 30 years. After an incubation period of between 1 and3 weeks the patient develops symptoms suggestive of viralpneumonia, with systemic upset, arthralgia and myalgiabeing particularly common.

Typically, the white cell countis not raised. The appearances on chest X-ray are very variable,and although segmental and subsegmental shadowsare most common, a lobar pattern can also be seen.In mycoplasma pneumonia cold agglutinins are presentin approximately 50% of cases and serological investigationsdemonstrate antibodies to mycoplasma in mostinstances.

Mycoplasma titres may be raised for severalyears following infection.The most effective therapy for mycoplasma infection iserythromycin, tetracycline or doxycycline. Complicationscan include a haemolytic anaemia and renal failure, owingto the presence of cold agglutinins, as well as meningism,central nervous system involvement and myocarditis. Formost patients the prognosis is excellent.

Psittacosis and ornithosis

Chlamydia psittaci infection is transmitted from parrotsto humans (psittacosis) or from other birds to humans(ornithosis). The organism (intermediate between a virusand a rickettsial organism and an obligate intracellularbacterium) is in the dust derived from excreta and feathers.The birds do not always appear to be ill. There isusually a history of close contact with birds (e.g. pigeonracers). The ensuing illness is rather like influenza. Thereis a cough, mucoid sputum, and sometimes haemoptysis.The chest X-ray shows patchy consolidation. A complicatingbacterial pneumonia is common.

Diagnosis is bestmade by a rising titre for chlamydia antibodies, and effectivetreatment is tetracycline or doxycycline. Erythromycinmay be used if these drugs are contraindicated.Chlamydia pneumoniae causes a pneumonia, usually inyoung adults within the community, similar to mycoplasmapneumonia. Diagnosis is serological and therapy is thesame as for psittacosis.

Rickettsial pneumonia (Q fever)

The rickettsial organism (Coxiella burnetii) is transmittedfrom animals (most commonly cattle and sheep) to humansby dust inhalation. Slaughterhouse workers are most ofteninfected. There is an abrupt onset of a viral-like illness withheadache and meningism. Respiratory symptoms are lessprominent. The chest X-ray shows patchy consolidation.

Diagnosis is confirmed by a rising antibody titre. A prolongedcourse of tetracycline (or erythromycin, combinedwith rifampicin in severe cases) is effective, as is chloramphenicol.Rickettsia can cause endocarditis.

Treatment of community acquired pneumoniaBecause of the likely pathogens, patients respond wellto a macrolide antibiotic (e.g. erythromycin or clarithromycin)plus, if systemically unwell, amoxycillin.

Hospital-acquired(nosocomial) pneumonia

Up to 5% of patients admitted to hospital for other causessubsequently develop a pneumonia. Particularly importantpredisposing factors are cigarette smoking, chroniclung disease, advanced age, obesity, the effects ofanaesthesia and surgery, and prior use of broad-spectrum antibiotics.The causative organisms for hospital-acquired pneumonias are different from those responsible for communityacquiredpneumonia and, in particular, Gram-negativeorganisms are responsible for 50% of cases. Anaerobic infections are also important.

The prior use of broad-spectrum antibiotics and theconsequent colonization of the oropharynx with Gramnegativebacilli reduces the value of sputum culture andmakes it difficult to find the cause of hospital-acquiredpneumonias. The management of these pneumoniasinvolves close collaboration between clinical staff andmicrobiologists. Gram stain of the sputum may be moreuseful than culture. Blood cultures will be positive in up to25% of cases.

Recurrent pneumonia

Prior to making a diagnosis of recurrent pneumonia, thepossibility of a non-infective cause of recurrent pulmonaryproblems should be considered. Alternative diagnoses willinclude pulmonary infarction, pulmonary eosinophilia(including bronchopulmonary aspergillosis) and asthma.

Aspiration pneumonia

Infection is usually with anaerobic organisms derivedfrom the upper respiratory tract. Aspiration pneumoniamay be acute, extensive and progressive, or it may runa more subacute course and progress to lung abscessformation.When cavitating anaerobic pneumonias communicatewith the bronchial tree the sputum is both copious andfoul-smelling.

The site of the pneumonia or lung abscesswill depend on the position of the patient at the time ofaspiration. Aspirated material enters the right lung moreeasily than the left, and will enter the lower lobes when the subject is standing, and the apical segment of the lowerlobes or the posterior segment of the upper lobes whensupine.An important cause of anaerobic pneumonias and lungabscess is bronchial obstruction (e.g. with bronchogeniccarcinoma), and if the diagnosis of aspiration is indoubt bronchoscopy is indicated. Radiological studies ofswallowing will frequently be rewarding.

Anaerobic infection causes considerable tissue destruction, with abscessformation, and empyema and metastatic abscesses can alsooccur. Prompt treatment avoids such problems. Mostupper respirating tract anaerobes are sensitive to penicillin.Early aspiration pneumonias are adequately treatedwith amoxycillin, but more severe infections and lungabscesses require parenteral cefuroxime and metronidazoleinitially, followed by oral amoxycillin and metronidazole(depending on cultures). Postural drainage isimportant, and antibiotic therapy should be continued for 6 weeks or more to minimize lung destruction.