Lower Respiratory Tract Infections

Acute Bronchitis

The vast majority of episodes of acute bronchitis infections are caused by viruses e.g. influenza viruses, RSV, adenoviruses, etc.  There are no reports in the literature to suggest that such patients benefit from antibiotics; therefore therapy should be symptomatic.  During outbreaks of Mycoplasma pneumoniae or Chlamydia pneumoniae infection, prescription of a macrolide or a tetracycline can be considered.

Acute exacerbations of chronic bronchitis

Viruses are often implicated, at least initially.  Secondary infections by bacteria such as Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae may be involved when sputum becomes purulent and increases in volume.  Although most clinicians treat patients in this setting with antibiotics, most studies comparing antibiotics with placebo have shown little difference in the rate of resolution of symptoms.   If antibiotics are prescribed, these should be based on the culture and sensitivity results and should be given for 7 - 10 days.   Amoxycillin-clavulanate, cefuroxime axetil or loracarbef may be considered initially for empiric antibiotic therapy.

Pneumonia

When the cause of pneumonia is known, the clinician will seldom have difficulty in deciding what to prescribe; it is therefore recommended that in severe cases, blood cultures and sputum (or other respiratory secretions) be submitted for microscopy and culture.  However empiric antibiotic therapy is usually given while waiting for laboratory results.   The choice varies according to the age of the patient, the severity of the illness and presence of any underlying illness.

o             Community-acquired pneumonia (CAP)

          (i)      Outpatient and inpatient treatment in patients less than 60 years without underlying disease

Streptococcus pneumoniae is by far the commonest cause of CAP. Amoxycillin 1000 mg orally 8 hourly (80 - 100 mg/kg/day in children)
                             OR
Ampicillin 1000 mg IV 6 hourly (200 mg/kg/day in children)
                             OR
Penicillin VK 1000 mg orally 6 hourly or penicillin G 2 - 4 mU 6 hourly IV (100000 units/kg/day in children)

Treat for at least 5 days or 36 - 48 hours after the temperature has normalised.

Alternative, but more expensive agents are erythromycin, clarith-romycin, azithromycin (these agents should ideally be used during mycoplasma epidemics) OR cefuroxime axetil.  In general, the use of macrolides for empiric therapy, should be discouraged since studies have documented similar outcomes in patients treated with penicillins compared to macrolides in the setting of large numbers of "atypical" infections. Suggestions that macrolides may be more attractive in the setting of penicillin-resistant pneumococci is unfounded, since macrolide resistance parallels penicillin resistance amongst pneumococcal isolates and may indeed by encountered in penicillin-sensitive isolates. There is little or no place for routine use of oral or parenteral third-generation cephalosporins such as cefpodoxime, ceftibutin or cefixime for CAP in this age group.

          (ii)     Patients more than 60 years and/or those with underlying illness/comorbidity

Cefuroxime  +/- erythromycin
                             OR
Amoxycillin-clavulanate +/- erythromycin

These agents should be given parenterally initially and replaced with oral agents once the temperature has settled. Treat for a total of 5 - 10 days.  Although some authorities recommend the addition of an amino-glycoside in suspected Pseudomonas aeruginosa infections, studies in South Africa have shown that Pseudomonas aeruginosa is rarely encountered in this group of patients, while Klebsiella pneumoniae is more often seen.   The majority of Klebsiella spp, especially in the com-munity setting, are susceptible to cefuroxime and amoxycillin-clavu-lanate.

          (iii)    Severely ill patients

As a generalisation, the presence of two or more of the parameters listed below indicate severe illness:

Clinical features:

o             confusion/decreased consciousness

o             low blood pressure (systolic < 90 mmHg, diastolic < 60 mmHg)

o             respiratory rate > 30 breaths/minute

o             multilobar consolidation

o             extrathoracic systemic complications

o             comorbid disease

Laboratory parameters –

o             hypoxaemia (pO2 < 8 kP)

o             white cell count < 4 or > 30 x 109/l

o             abnormal renal function (e.g. urea > 7 mmol/l)

o             abnormal liver function (e.g. albumin < 30 g/l)

o             rapidly expanding infiltrates

o             multilobar consolidation

o             cavitation.

                   Cefuroxime OR amoxycillin-clavulanate
                                    PLUS
                   Amikacin
                                    PLUS
                   Erythromycin
                   All agents are given parenterally for 2 - 3 weeks.

Note:  Because Pseudomonas aeruginosa is infrequently encountered in community-acquired pneumonia, empiric treatment with fourth-generation cephalosporins or carbapenems is not necessary.

o             "Atypical pneumonia "

Usually caused by Mycoplasma pneumoniae, Chlamydia pneumoniae or rarely Legionella spp.

Erythromycin 500 mg 6 hourly ( 30 - 50 mg/kg/day in children)
                           OR
Roxithromycin 150 mg 12 hourly (5 - 10 mg/kg/day in children)
                           OR
Clarithromycin 250 mg 12 hourly
                           OR
Azithromycin 250 mg daily
                           OR
Tetracycline 500 mg 6 hourly
                           OR
          Doxycycline 100 mg 12 hourly. 

Treat for 7 - 10 days for mycoplasma and chlamydia, but for 21 days for legionella.

o             Pneumonia during influenza epidemics

Usually caused by  Staphylococcus aureus,  Streptococcus pneumoniae, or  Haemophilus influenzae. Treat with amoxycillin-clavulanate OR cefuroxime axetil OR cephalexin.   Adjust therapy once aetiology established.

o           Aspiration pneumonia

Usually due to anaerobes alone or with facultative or aerobic bacteria.  The most common aerobes in community-acquired cases are Streptococcus spp., whilst Gram-negative bacilli and Staphylococcus aureus are prominent in hospital-acquired aspiration pneumonia.

Metronidazole orally, rectally or IV PLUS amikacin IV
                           OR
Metronidazole orally, rectally or IV PLUS amoxycillin-clavulanate
                           OR
Metronidazole orally, rectally or IV PLUS cefuroxime OR cefotaxime.
Clindamycin can be used as an alternative to metronidazole.   Duration of therapy is based on clinical grounds.

o             Hospital-acquired pneumonia or pneumonia in the debilitated patient

In addition to the usual pathogens, also consider Gram-negative bacilli such as Pseudomonas aeruginosa, Acinetobacter spp., Klebsiella spp., Serratia spp. and staphylococci.

          Empiric regimens include:
          Ceftriaxone 2 g  IM once daily (25 - 50 mg/kg/day in children)
                        OR
          Cefotaxime 1 g IV 8 hourly (150 - 200 mg/kg/day in children)
                        OR
          Ceftazidime 1-2 g IV 8 hourly (90 - 150 mg/kg/day in children)
                        OR
          Cefepime 1 - 2 g 12 hourly OR cefpirome 2 g 12 hourly
                        PLUS
          Amikacin 15 mg/kg given IV once daily.

Alternate regimens include imipenem alone.  If the patient has notresponded within 48 hours to the above regimen, and there is a clinical suspicion of a staphylococcal infection, cloxacillin 2 g 4 hourly IV (150 -   200 mg/kg/day in children) or vancomycin 500 mg IV 12 hourly (40 mg/kg/day in children), should probably be added.  Therapy should be adjusted once results of cultures are available.

o             Pneumonia in the immunocompromised patient (e.g. AIDS)

In addition to other causes, also consider Pneumocystis carinii, fungi and Cytomegalovirus.  These patients require urgent specialist referral.