Pneumocystis jirovecii (previously Pneumocystis carinii)

Problem script 

Epi: immunocompromised (eg: HIV with CD4<200 or not on Bactrim PPX, hematologic malignancy s/p BMT)
Timing: Sub-acute (weeks)-contrast with acute bacterial PNA which is more acute!
S&S: Fever (>80 %), progressive exertional dyspnea (95 %), non-productive cough, CXR usually with bilateral infiltrates but can also cause PTX, can also see GGO on CT scan

Labs to support diagnosis but does not make the diagnosis

Elevated LDH (sensitive but not specific)
ABG-check degree of hypoxia and AA gradient
Elevated 1,3 beta-d-glucan-part of cell wall (sensitive but not specific)
HIV with CD4 count <200 (risk factor)

Imaging

CXR-classically bilateral interstitial/alveolar infiltrates but can be variable. Suspect PCP if spontaneous PTX in patient with PNA and risk factors for PCP!
CT–excellent sensitivity, can see bilateral patchy/nodular ground glass opacities (not necessary but can order CT if unclear diagnosis)

Making the diagnosis– must VISUALIZE cystic/trophic forms, PCP cannot be cultured 

Step 1: Sputum Induction (order specifically for PCP!), specificity of ~100 % but variable sensitivity of 55-90 %
 If negative and high suspicion for PCP, proceed to Step 2

Step 2: Bronchoalveolar Lavage, 90-100 % sensitivity, ~100 % specificity

Treatment

First line is Bactrim 15-20 mg/kg oral or IV TID/QID x 21d (remember Bactrim has good bioavailability!)-No need to hold treatment before making diagnosis if high suspicion!
Treat with adjunctive steroids if PaO2<70 or A-A gradient >35
                     Dosing: Prednisone 40 mg PO BID x 5d, 40 mg PO daily x 5d, 20 mg PO daily x 11d.

Remember that it can take several days to see response in treatment, can get worse before getting better!

Primary Prophylaxis in HIV patients