Board-Relevant Information: Bacterial and Viral Infections
Bacteroides fragilis
Bacteroides fragilis is a key anaerobic pathogen causing intra-abdominal, pelvic, and soft tissue infections with high propensity for abscess formation.
Clinical Significance
- Primary pathogen in intra-abdominal infections including peritonitis, intra-abdominal abscess, and liver abscess 1
- Causes gynecologic infections (endometritis, endomyometritis, tubo-ovarian abscess, postsurgical vaginal cuff infection) 1
- Responsible for skin and skin structure infections, bacterial septicemia, bone and joint infections, CNS infections (meningitis, brain abscess), lower respiratory tract infections (pneumonia, empyema, lung abscess), and endocarditis 1
- 47% of wound infections following intestinal surgery develop complications, usually abscess formation 2
Treatment
- First-line: Metronidazole for all Bacteroides fragilis infections 1, 3
- Metronidazole achieves serum levels several times the minimal inhibitory concentration and penetrates well into CSF 3
- For lung abscess or documented anaerobes: Add clindamycin or metronidazole to the primary regimen 4
- For multidrug-resistant B. fragilis (resistant to metronidazole, beta-lactams, carbapenems): Linezolid achieves microbiological cure 5
- Surgical drainage required for abscesses; metronidazole does not obviate need for aspiration or drainage 1
Abscess Formation and Healing
Anaerobic Abscess Management
- Bacteroides species have unusual propensity for abscess formation in wound infections following intestinal surgery 2
- Surgical drainage is mandatory in conjunction with antimicrobial therapy 1
- For liver abscess due to amebiasis or bacteria, metronidazole therapy does not eliminate need for aspiration or drainage 1
Bordetella pertussis
Clinical Presentation
- Median cough duration: 51 days when B. pertussis is the sole agent 6
- 82% of single-agent B. pertussis infections present with spasmodic cough for ≥21 days (WHO clinical criteria for pertussis) 6
- Co-infections with other respiratory pathogens extend cough duration to approximately 60 days 6
Diagnosis and Treatment
- Laboratory confirmation is essential for rational treatment; clinical diagnosis alone is insufficient 6
- Antibiotic treatment rates vary significantly by region (12-34% in studies) 6
- Acellular vaccines more efficient against serious disease than whole cell vaccines 6
Legionella pneumophila
Treatment in Community-Acquired Pneumonia
- Severe CAP requiring ICU admission: Beta-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) PLUS azithromycin or respiratory fluoroquinolone (moxifloxacin or levofloxacin 750 mg/day) 4
- Coverage for Legionella is mandatory in severe pneumonia along with pneumococcus and H. influenzae 4
- Macrolides or fluoroquinolones provide adequate Legionella coverage 4
HIV-Infected Patients
- ICU treatment: IV beta-lactam plus IV azithromycin OR IV respiratory fluoroquinolone 4
- Fluoroquinolones should be used cautiously if TB suspected but not being treated with four-drug therapy 4
Helicobacter pylori
No specific guideline or drug information provided in evidence
Mycoplasma pneumoniae
Clinical Characteristics
- Median cough duration: 23 days as single agent 6
- Only 26% present with spasmodic cough ≥21 days (lower than B. pertussis) 6
- Common cause of atypical pneumonia in HIV-infected population, likely underreported 7
Treatment
- First-line alternative (doxycycline-resistant): Azithromycin 500 mg orally day 1, then 250 mg once daily for 5 days 8
- Alternative options: Levofloxacin 750 mg orally or IV once daily for 7-14 days OR moxifloxacin 400 mg orally or IV once daily for 7-14 days 8
- For hospitalized patients with bacterial pneumonia: Add azithromycin to treat M. pneumoniae and Chlamydia pneumoniae 4
- Pregnant women should avoid doxycycline and fluoroquinolones; use macrolides instead 8
Antiviral Drugs Overview
HIV Drugs
NRTIs (Nucleoside Reverse Transcriptase Inhibitors)
No specific guideline or drug information provided in evidence
Protease Inhibitors
No specific guideline or drug information provided in evidence
Maraviroc (CCR5 Antagonist)
No specific guideline or drug information provided in evidence
Fusion Inhibitors and Integrase Inhibitors
No specific guideline or drug information provided in evidence
Interferons (Alpha, Beta, Gamma)
No specific guideline or drug information provided in evidence
Ribavirin
No specific guideline or drug information provided in evidence
Sofosbuvir
No specific guideline or drug information provided in evidence
Simeprevir
No specific guideline or drug information provided in evidence
Acyclovir, Valacyclovir, Famciclovir
No specific guideline or drug information provided in evidence
Ganciclovir, Valganciclovir
- For CMV infection in HIV-infected children: Treatment duration and dosing per CDC/NIH guidelines 4
- Used for CMV infection in outpatient parenteral antimicrobial therapy 4
Foscarnet
No specific guideline or drug information provided in evidence
Cidofovir
No specific guideline or drug information provided in evidence
Prion Disease
No specific guideline or drug information provided in evidence
Delirium
No specific guideline or drug information provided in evidence
Dementia
No specific guideline or drug information provided in evidence
Klebsiella pneumoniae
Clinical Context
- Common co-pathogen with Bacteroides fragilis in wound infections following intestinal surgery 2
- Requires aerobic antimicrobial coverage in mixed aerobic-anaerobic infections 1
Enterobacter species
Clinical Context
- Co-pathogen with Bacteroides fragilis in postoperative wound infections 2
- Requires appropriate aerobic coverage in addition to anaerobic therapy 1
Serratia marcescens
No specific guideline or drug information provided in evidence
Haemophilus influenzae
Treatment in Severe CAP
- Severe CAP therapy must cover H. influenzae along with pneumococcus and Legionella 4
- Beta-lactams active against DRSP (drug-resistant S. pneumoniae) provide adequate H. influenzae coverage 4
- For HIV-infected patients with severe pneumonia: IV beta-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) plus macrolide or fluoroquinolone 4
Head and Neck Infections
Specific Infections
- Complicated sinusitis: Treated with outpatient parenteral antimicrobial therapy 4
- Chronic otitis and/or mastoiditis: Managed with OPAT 4
- Brain or epidural abscess: Requires combination antimicrobial therapy and surgical drainage 4
HIV/AIDS
Bacterial Pneumonia in HIV
- Outpatient treatment: Respiratory fluoroquinolone (moxifloxacin, levofloxacin 750 mg/day, or gemifloxacin) for penicillin-allergic patients or recent beta-lactam exposure 4
- Macrolide monotherapy cannot be routinely recommended due to increasing pneumococcal resistance 4
- Patients on MAC prophylaxis should never receive macrolide monotherapy for empiric bacterial pneumonia treatment 4
Non-ICU Inpatient Treatment
- IV beta-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) plus macrolide 4
- Doxycycline is alternative to macrolide 4
ICU Treatment
- IV beta-lactam plus IV azithromycin OR IV respiratory fluoroquinolone 4
- For penicillin allergy: Aztreonam plus IV respiratory fluoroquinolone 4
Pseudomonas Coverage in HIV
- If risk factors present: Antipneumococcal, antipseudomonal beta-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) plus ciprofloxacin or levofloxacin 750 mg 4
- Alternative: Beta-lactam plus aminoglycoside and azithromycin 4
MRSA Coverage in HIV
- If risk factors present: Add vancomycin (possibly with clindamycin) or linezolid 4