Pneumonia 【肺炎】

說到 Infectious Diseases，就不得不提到這個經典中的經典 － Pneumonia【PNA】

肺炎的定義：簡單來說就是肺部組織受到感染。

那是如何進到我們肺部呢？我們就要把肺炎細分為以下4大類：

< Microbiology of Pneumonia >

1. Community-acquired pneumonia (CAP)

• S. pneumonia
• Mycoplasma, Chlamydia, viral (esp. in young & healthy)
• H. influenzae, M. catarrhalis (esp. in COPD)
• Legionella (esp. in elder, smoker, ↓ immunity, TNF inhibitors)
• Klebsiella & other GNR (esp. in alcoholics & aspirators)
• S. aureus (esp. postiviral infection)

2. Hospital-acquired pneumonia or Health care-associated pneumonia (HAP/HCAP)

• GNR including Pseudomonas, Klebsiella, E. coli, Enterobacter, Serratia, Acinetobacter
• S. aureus (including MRSA)
• Acid suppression may ↑ risk of acquiring PNA － 說穿了就是 PPI, H2 blocker....

3. Aspiration pneumonia

• Chemical pneumonia due to aspiration of gastric contents
• Bacterial pneumonia ≧24-72 hrs later, due to aspiration of oropharyngeal [口咽] microbes

            - outPt: typical oral oral flora (strep [鏈球菌], S. aureus, anaerobes [厭氧菌])

            - inPt or chronically ill: GNR and S. aureus

4. Immunosuppressed pneumonia → 『非本章重點，可先不記』

• Above + PCP, fungi, Nocardoa, non-TB mycobacteria, CMV, HSV

< Clinical manifestations >

• "Typical [典型]": acute onset of fever, cough帶濃痰, dyspnea [呼吸困難], Chest X-ray (CXR) 呈現 consolidation [實質化]
• "Atypical [非典型]": dry cough 或陣發性刺激性咳嗽, 肺外症狀居多 (nausea and/or vomiting, diarrhea [腹瀉], myalgias [肌肉痠痛], sore throat [喉嚨痛]), 在 CXR 會呈現 patchy interstitial pattern [斑片狀間質性型態], 一般不引起肺部實變及胸腔積液
• 病徵、症狀和影像學檢查都無法可靠地區分 "typical" (S. pneumo, H. flu) 和 "atypical" (Mycoplasma, Chlamydia, Legionella, viral) 兩者差異
• Legionella 會使 ↑ aminotransferases & ↓ Na (50-70% 呈現低鈉血症, 尤其 < 130 mmol/L)

Treatment

1. Outpatient

• No recent abx; macrolide or doxycycline
• Recent abx or comorbidities [共病症] (eg, cardiopulm, hepatorenal, DM, EtOH); respiratory FQ or (macrolide + [high-dose amox ± clav or 2nd-gen ceph.]) 

2. Community-acquired, inpatient

• (3rd-gen ceph. + macrolide) or respiratory FQ
• MRSA coverage, if necrotizing [壞死性] or with empyema [積膿] (罕見)

3. Community-acquired, inpatient, ICU

• (3rd-gen ceph. or amp-sulbactam) + (macrolide or FQ) (假設 no risk for Pseudomonas)

4. Hosp-acquired & risk for MDR pathogens

• (Antipseudomonal PCN or ceph. or carbapenem) + (FQ or [gentamicin + azithromycin]) + MRSA coverage

5. Immunosppressed

• As Above ± TMP-SMX ± steroids to cover PCP

6. Aspiration

• (3rd-gen ceph. or FQ) ± (clindamycin or metronidazole)

Empirical Antibiotic Treatment

Outpatients

Previously healthy and no antibiotics in past 3 months l   A macrolide (clarithromycin [500 mg PO bid] or azithromycin [500 mg PO once, then 250 mg qd]) or l   Doxycycline (100 mg PO bid)

Comorbidities or antibiotics in past 3 months: select an alternative from a different class l   A respiratory fluoroquinolone (moxifloxacin [400 mg PO qd], gemifloxacin [320 mg PO qd], levofloxacin [750 mg PO qd]) or l   A β-lactam (preferred: high-dose amoxicillin [1 g tid] or amoxicillin/clavulanate [2 g bid]; alternatives: ceftriaxone [1–2 g IV qd], cefpodoxime [200 mg PO bid], cefuroxime [500 mg PO bid]) plus a macrolidea

In regions with a high rate of“high-level”pneumococcal macrolide resistance,b consider alternatives listed above for patients with comorbidities.

Inpatients, Non-ICU

l   A respiratory fluoroquinolone (e.g., moxifloxacin [400 mg PO or IV qd] or levofloxacin [750 mg PO or IV qd]) l   A β-lactamc (e.g., ceftriaxone [1–2 g IV qd], ampicillin [1–2 g IV q4–6h], cefotaxime [1–2 g IV q8h], ertapenem [1 g IV qd]) plus a macrolided (e.g., oral clarithromycin or azithromycin [as listed above] or IV azithromycin [1 g once, then 500 mg qd])

Inpatients, ICU

l   A β-lactame (e.g., ceftriaxone [2 g IV qd], ampicillin-sulbactam [2 g IV q8h], or cefotaxime [1–2 g IV q8h]) plus either azithromycin or a fluoroquinolone (as listed above for inpatients, non-ICU)

Special Concerns

If Pseudomonas is a consideration: l   An antipseudomonal β-lactam (e.g., piperacillin/tazobactam [4.5 g IV q6h], cefepime [1–2 g IV q12h], imipenem [500 mg IV q6h], meropenem [1 g IVq8h]) plus either ciprofloxacin (400 mg IV q12h) or levofloxacin (750 mg IV qd) l   The above β-lactams plus an aminoglycoside (amikacin [15 mg/kg qd] or tobramycin [1.7 mg/kg qd]) plus azithromycin l   The above β-lactamsf plus an aminoglycoside plus an antipneumococcal fluoroquinolone If CA-MRSA is a consideration: l   Add linezolid (600 mg IV q12h) or vancomycin (15 mg/kg q12h initially, with adjusted doses)

註： aDoxycycline (100 mg PO bid) is an alternative to the macrolide. bMICs of >16 μg/mL in 25% of isolates. cA respiratory fluoroquinolone should be used for penicillin-allergic patients. dDoxycycline (100 mg IV q12h) is an alternative to the macrolide. eFor penicillin-allergic patients, use a respiratory fluoroquinolone and aztreonam (2 g IV q8h). fFor penicillin-allergic patients, substitute aztreonam. Abbreviations: CA-MRSA, community-acquired methicillin-resistant Staphylococcus aureus; ICU, intensive care unit.