CAP Challenge!

The most likely cause is Streptococcus pneumoniae.

We are classically taught that lobar consolidation is typical of pneumonococcal pneumonia and that atypicals cause a more diffuse bronchopneumonia. In the real world this is not always true.

Other common causes of adult community-acquired pneumonia include:

Mycoplasma pneumoniae
Chlamydia pneumoniae
Legionella pneumophila
Haemophilis influenzae
Staphylococcus aureus
Respiratory viruses

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Antibiotic recommendations for PSI severity Class 1 and 2 are the same:

Oral amoxicillin (has better activity than oral phenoxypenicillin against H. influenzae).
Doxycycline or a macrolide (e.g. roxithromycin) could be added to cover for atypicals like Mycoplasma pneumoniae and Chlamydia spp.

Some observational studies suggest better outcomes for pneumococcal pneumonia when beta-lactams are combined with macrolides or doxycycline. Penicillin-resistant pneumococci and H. influenzae are currently rare in Australia (in contrast to North America, where fluoroquinolones may be required as first line due to penicillin-resistant pneumococci).

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Cephalosporins (such as oral cefuroxime) are safe alternatives in the absence of immediate hypersensitivity (urticaria, angioedema, bronchospasm or anaphylactic shock) or Stevens-Johnson Syndrome.

Alternatively, doxycycline or a macrolide could also be used alone (in the United States about 30% of pneumococci are macrolide-resistant).

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He has penicillin-resistant pneumococcal pneumonia

Pneumococci with an MIC <2mg/L can be treated with standard doses of penicillins, whereas those with an MIC>2mg/l cannot as they lack full susceptibility to penicillin. Antibiotic selection should be as advised by an infectious diseases specialist. Vancomycin and fluoroquinolones are options.

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Young hypoxic patients with no comorbidities – especially those that have widespread infiltrates on their chest radiographs.

The PSI score has been criticized as a means for triaging CAP patients to site of care and antibiotic selection. It is heavily weighted to age and comorbidities. In the cohort used to validate the PSI (Fine et al, 1997) only about a third of patients requiring ICU level care had Class 5 severity pneumonia. It is better at determining which patients can be successfully managed on an outpatient basis.

Warning: excessive discussion of various CAP prediction rules follows…

Given the relatively poor prediction of ICU admission, some authorities have suggested that PSI Class 4 severity patients should be treated with same antibiotics as PSI Class 5. Others have suggested that the CURB score (aka the modified British Thoracic Society (mBTS) Severity Score) better predicts which patients need ICU admission. More recently, the CURB65 score (with a variant the CRB65 score if urea is not available) was validated internationally and was comparable to mBTS with the advantage of better stratification of patients suitable for outpatient management.

The CURB65 algorithim (from Lim et al, 2003). Click to enlarge.

More recent studies have suggested that CURB65 and PSI are comparable prediction tools, although CURB65 is a simpler rule (see references below). Neither excel at identifying patients requiring ICU admission. The SMART-COP rule was developed with this purpose in mind, and has been modified for use in tropical Australia (SMARTACOP). Unfortunately none of these rules are perfect and clinical judgment is paramount in the management of patients with potentially severe CAP.

Regardless of the scoring system used, it is prudent to consider the young, sick, hypoxic pneumonia patient with bilateral or multifocal infiltrates as a severe case.

Legionella pneumophila type 1

This is the commonest cause of Legionella pneumonia. Other types of  Legionella (including L. longbeachae, an occasional cause of CAP in Australia) are not detected by the urine antigen assay.
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Options include:

Macrolides such as azithromycin 500mg IV or po daily
or
Doxycycline 100mg IV or po bd

Total duration of treatment is for 7-14 days in the immunocompetent and 14-21 days in the immune suppressed. Note that IV administration of doxycycline is painful and oral administration has similar bioavailability.
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Change to IV administration of a macrolide (or doxycycline) as gastrointestinal absorption is impaired by vomiting.

Severe cases of Legionella pneumonia should also have added either of:

Ciprofloxacin 400mg IV or 750mg po q12h
or
Rifampicin 600mg IV or po od

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Either benzylpenicillin IV (1.2g q6h) or amoxicillin IV (1g q6h) until improving clinically, followed by amoxicillin 1g po q8h for a total of 7 days.
and
Either doxycycline 100mg po for 7 days or a macrolide such as roxithromycin 300mg od for 5 days

Patients in tropical Australia with no risk factors (see below) are treated with the same antibiotics as those in non-tropical Australia. Class 3 and 4 severity CAP are treated with the same antibiotic regimes.

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Either add gentamicin
or change penicillin/ amoxicillin to a third -generation cephalosporin (ceftriaxone or cefotaxime).

Gram-negative pathogens, including Klebsiella pneumoniae and Pseudomonas aeruginosa, are more likely to be present in  severe CAPs and in those with risk factors.

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Moxifloxacin 400mg po od for 7 days

Moxiflxacin is a ‘fourth generation’ fluorquinolone. It differs to ciprofloxacin in that is has excellent activity against streptococci (including S. pneumoniae), staphylococci (except MRSA) and anaerobes, but is less active against P. aeruginosa.

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Ceftriaxone 2g IV q24h and gentamicin 4-6 mg/kg IV stat are given for Class 3 and 4 severity CAP in tropical Australia if risk factors are present.

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Burkholderia pseudomallei (melioidosis) and Acinetobacter baumanii are important causes of CAP in tropical Australia

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Risk factors include:

Alcoholism
Diabetes
Chronic renal failure
COPD

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Ashdown’s medium contains crystal violet and gentmicin – it is used to selectively grow Burkholderia pseudomallei.

Her antibiotics should be changed to ceftazidime 2g IV for at least 14 days.

If she deteriorates and requires ICU admission this should be changed to meropenem 1g q8h. G-CSF may be given although its efficacy is uncertain.

Patients with meliodosis require at least 3 months of eradication therapy following the initial intensive antibiotic treatment:

trimethoprim+sulfamethoxazole 320+1600 mg bd po (with folic acid 5 mg od)
+/- doxycycline 100 mgbd po

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Severe CAP requiring ICU admission requires broad spectrum coverage in the first instance:

azithromycin 500 mg IV, daily

and either:

a third generation cephalosporin (ceftriaxone 1 g IV q24h or cefotaxime 1 g IV q8h)

or

benzylpenicillin 1.2 g IV q4h and gentamicin 4 to 6 mg/kg IV q24h
(again, moxifloxacin may be used if there is immediate hypersensitivity to penicillin)

In tropical Australia, melioidosis must be covered so that appropriate combination is:

Meropenem 1g q8h IV and azithromycin 500mg q24h IV

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Staphylococcus aureus

This organism may be cause pneumonia primarily, or pneumonia may follow an influenza-like illness, aspiration or occur in the context of endocarditis.

Severely ill patients (as well as those with immediate sensitivity to penicillin) should be treated with:

vancomycin 25mg/kg up to 1g bd IV (rather than flucloxacillin 2g IV q6h) due to the possibility of MRSA.

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Community acquired MRSA in Australia is more common in certain populations. At risk groups include:

• IV drug users
• indigenous Australians
• Pacific Islanders

Community acquired MRSA may be more virulent than hospital-acquired MRSA due to the presence of the Panton-Valentine leucocidin [PVL] virulence factor. However, susceptibility testing is vital as community-acquired MRSA is more likely to be susceptible to other antibiotics such as clindamycin and cotrimoxazole.

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