Infectious Disease Compendium

Lung Abscess

Diagnosis

Fevers, weight loss, cough productive of the worst smelling sputum on the planet. CXR has a usually thick-walled cavity with an air-fluid level, often it erodes into pleural space to cause an empyema.

If you have never smelled an anaerobic pneumonia, mix a pound of hamburger with some stool and spit and put it in a sealed bag in a warm place for a week. Open, sniff, then barf. It is a rotten stench beyond foul. You can often smell the rot from the doorway.

Epidemiologic Risks

Poor dentition and loss of consciousness (from trauma, ETOH, drugs or seizures) with resultant aspiration.

Lung abscess is the real, and only, aspiration pneumonia where anaerobes are a pathogen. In all aspiration events, whether in the community, the hospital or the ventilated patients, anaerobes are never, ever (that is a never and an ever) an issue and never ever need to be treated.

Microbiology

Bacterial: classically these are mixed infections with viridans, especially S. anginosus group, and other streptococci, Peptostreptococcus, Bacteroides, and oral anaerobes (Pubmed).

Many other organisms can cause cavitary pneumonia including, but not limited to, Actinomyces, Aspergillus, Blastomyces, Coccidioides, Corynebacterium pseudodiphtheriticum, Cryptococcus, Echinococcus, Entamoeba histolytica, Histoplasma, Legionella, Mycobacteria, Nocardia, Paragonimus westermani, Pneumocystis (especially on inhaled pentamidine), Pseudomonas aeruginosa, Staphylococcus aureus, Zygomycetes.

Empiric Therapy

Penicillin G or ampicillin PLUS metronidazole (my favorite); a third-generation cephalosporin (could substitute for the ampicillin) PLUS metronidazole OR penicillin/beta-lactamase inhibitors OR clindamycin OR cefoxitin OR cefotetan OR a quinolone PLUS metronidazole.

For a classic lung abscess, my go-to in-house is ceftriaxone and oral metronidazole. Outhouse? If nothing odd or resistant oral amoxicillin and metronidazole. If I don't like the patient I suggest Augmentin: costs a lot more and will almost certainly cause diarrhea.

The endpoint is a cure, which is often radiographic and can take weeks.

For the treatment of other causes, see the specific organism.

If antibiotics fail, percutaneous drainage can help with little in the way of morbidity (PubMed).

Pearls

No teeth, no anaerobes. Anaerobic lung abscess in those with no teeth is due to lung cancer.

Given the increased resistance of streptococci and anaerobes to clindamycin (both around 30%), I no longer use it. Once therapy is begun, expect fevers for at least 10 - 14 days.

Rants

Classically aspiration pneumonia is a lung abscess in people with poor dentition and loss of consciousness. In those cases, anaerobes play a role and are the sequela of a relatively chronic process.

In acute aspiration, studies of outpatients, hospital, and ventilator aspiration events have consistently failed to find anaerobes and they do not need to be treated.

No guideline suggests treating anaerobes in an acute aspiration, based in part on the following and whether antibiotics are even needed is a question, although differentiating aspiration from pneumonia is always difficult.

So while treating acute aspiration with antibiotics is problematic, treating acute aspiration with anti-anaerobic antibiotics is usually stupid.

Prophylactic Antimicrobial Therapy for Acute Aspiration Pneumonitis

Clinical Infectious Diseases, Volume 67, Issue 4, 1 August 2018, Pages 513–518,

Abstract Background Prophylactic antimicrobial therapy is frequently prescribed for acute aspiration pneumonitis, with the intent of preventing the development of aspiration pneumonia. However, few clinical studies have examined the benefits and harms of this practice.

Methods A retrospective cohort study design was used to compare outcomes of patients with aspiration pneumonitis who received prophylactic antimicrobial therapy with those managed with supportive care only during the initial 2 days following macro-aspiration. The primary outcome was in-hospital mortality within 30 days. Secondary outcomes included transfer to critical care and antimicrobial therapy received between days 3 and 14 following macroaspiration including escalation of therapy and antibiotic-free days.

Results Among 1483 patients reviewed, 200 met the case definition for acute aspiration pneumonitis, including 76 (38%) who received prophylactic antimicrobial therapy and 124 (62%) who received supportive management only. After adjusting for patient-level predictors, antimicrobial prophylaxis was not associated with any improvement in mortality (odds ratio, 0.9; 95% confidence interval [CI], 0.4–1.7; P = .7). Patients receiving prophylactic antimicrobial therapy were no less likely to require transfer to critical care (5% vs 6%; P = .7) and subsequently received more frequent escalation of antibiotic therapy (8% vs 1%; P = .002) and fewer antibiotic-free days (7.5 vs 10.9; P < .0001).

Conclusions Prophylactic antimicrobial therapy for patients with acute aspiration pneumonitis does not offer clinical benefit and may generate antibiotic selective pressures that results in the need for escalation of antibiotic therapy among those who develop aspiration pneumonia.

NEJM Review Review Article

Primary Care Aspiration Pneumonitis and Aspiration Pneumonia

"In two studies performed in the 1990s, sampling of the lower respiratory tract with a protected specimen brush, followed by quantitative and anaerobic culturing of the specimens, was performed in patients with acute aspiration syndromes. Mier and colleagues studied 52 patients admitted to an intensive care unit with a diagnosis of aspiration pneumonia. Bacterial pathogens were isolated in substantial concentrations (?1000 colony-forming units per milliliter) from only 19 patients, and the spectrum of organisms identified depended on whether the aspiration syndrome was community acquired or hospital acquired. Strep. pneumoniae, Staph. aureus, H. influenzae, and Enterobacteriaceae predominated in patients with a community-acquired aspiration syndrome, whereas gram-negative organisms, including P. aeruginosa, predominated in patients with a hospital-acquired aspiration syndrome. No anaerobic organisms were isolated. In a similar study, in which sampling with a protected specimen brush was performed in a blinded fashion in 25 patients with gastric aspiration, bacterial pathogens were isolated from 12 patients, 8 of whom had risk factors for gastric colonization (small-bowel obstruction or ileus, the presence of a feeding tube, or therapy with histamine H2 antagonists). The spectrum of pathogens was similar to that reported by Mier and colleagues, and no pathogenic anaerobic organisms were isolated.

The role of anaerobes in patients with ventilator-associated pneumonia and aspiration pneumonia: a prospective study.

CONTEXT: Aspiration of oropharyngeal material, with its high concentration of anaerobic bacteria, has been implicated in the pathogenesis of both ventilator-associated pneumonia (VAP) and aspiration pneumonitis (AP). Consequently, patients with these disorders are usually treated with antimicrobial agents with anaerobic activity.

OBJECTIVE: To determine the incidence of anaerobic bacteria in patients with VAP and AP. DESIGN: Prospective, nonrandomized, interventional study. SETTING: University-affiliated community teaching hospital.

PATIENTS AND INTERVENTIONS: We performed sequential blind protected specimen brush (PSB) sampling and mini-BAL in 143 patients with 185 episodes of suspected VAP and 25 patients with AP who required mechanical ventilation. Quantitative aerobic and anaerobic cultures were performed on all specimens. Pneumonia was considered to be present when either > 500 cfu/mL cultured from blind PSB sampling or > 5,000 cfu/mL cultured from mini-BAL were present.

RESULTS: Using the predefined criteria, bacterial pneumonia was diagnosed in 63 of 185 suspected VAP episodes (34%) and 12 of 25 patients with AP (48%). At least one dose of an antibiotic was given in the 24 h prior to bacteriologic sampling in 106 suspected VAP episodes (57%) and in 12 patients with AP (48%). More than one pathogen was isolated from 11 VAP and four AP patients. Pseudomonas aeruginosa, Staphylococcus aureus, and enteric Gram-negative organisms were isolated most frequently from patients with VAP. In the patients with AP, enteric Gram-negative organisms were isolated in patients with GI disorders and Streptococcus pneumoniae and Haemophilus influenzae predominated in patients with "community-acquired" aspiration. Only one anaerobic organism was isolated from the entire group of patients; Veillonella paravula was isolated from a blind PSB specimen in a patient with suspected aspiration pneumonia.

CONCLUSION: Despite painstaking effort, we were able to isolate only one anaerobic organism (nonpathogenic) from this group of patients. The spectrum of aerobes in patients with VAP was similar to that reported in the literature. The organisms found in patients with AP was a reflection of the organisms likely to colonize the oropharynx. The use of antibiotics with anaerobic coverage may not be necessary in patients with suspected VAP and AP. Furthermore, penicillin G and clindamycin may not be the antibiotics of choice in patients with AP.

Bacteriology of aspiration pneumonia in patients with acute coma. Lauterbach E1, Voss F, Gerigk R, Lauterbach M. Author information

Abstract Loss of protective airway reflexes in patients with acute coma puts these patients at risk of aspiration pneumonia complicating the course of the primary disease. Available data vary considerably with regard to bacteriology, role of anaerobic bacteria, and antibiotic treatment. Our objective was to research the bacteriology of aspiration pneumonia in acute coma patients who were not pre-treated with antibiotics or hospitalized within 30 days prior to the event. We prospectively analyzed 127 patient records from adult patients admitted, intubated and ventilated to a tertiary medical intensive care unit with acute coma. Bacteriology and antibiotic resistance testing from tracheal aspirate sampled within 24 h after admission, blood cultures, ICU scores (APACHE II, SOFA), hematology, and clinical chemistry were assessed. Patients were followed up until death or hospital discharge. The majority of patients with acute coma suffered from acute cardiovascular disorders, predominantly myocardial infarction, followed by poisonings, and coma of unknown cause. In a majority of our patients, microaspiration resulted in overt infection. Most frequently S. aureus, H. influenzae, and S. pneumoniae were isolated. Anaerobic bacteria (Bacteroides spec., Fusobacteria, Prevotella spec.) were isolated from tracheal aspirate in a minority of patients, and predominantly as part of a mixed infection. Antibiotic monotherapy with a 2nd generation cephalosporin, or a 3rd generation gyrase inhibitor, was most effective in our patients regardless of the presence of anaerobic bacteria.

Am J Infect Control. 2013 Oct;41(10):880-4. doi: 10.1016/j.ajic.2013.01.007. Epub 2013 Mar 22. microbiology and prognostic factors of hospital- and community-acquired aspiration pneumonia in respiratory intensive care unit.

Abstract BACKGROUND: Incidence of aspiration pneumonia in hospital-acquired pneumonia and community-acquired pneumonia is high; however, many features of this disease remain imprecise. Our objective was to characterize the microbial etiology and their antibiotic resistance and to determine the prognostic factors in aspiration pneumonia among patients admitted to a respiratory intensive care unit (RICU).

METHODS: A prospective survey was conducted in 112 patients exhibiting hospital-or community-acquired aspiration pneumonia in the RICU of a provincial general hospital from 2010-2012. Bronchoalveolar lavage sampling was collected, and then followed by standard culture and drug-sensitive test. Risk factors were analyzed by multivariate logistic analysis.

RESULTS: One hundred twenty-eight strains were isolated in 94 patients, gram-negative bacilli (57.8%) was the predominant cultured microorganism, followed by fungus (28.9%) and gram-positive cocci (13.3%). The 5 main isolated bacteria demonstrated high and multiantibiotic resistance. The crude overall mortality was 43.8%, 50%, and 40%, respectively, in hospital- and community-acquired aspiration pneumonia group. Multivariate logistic analysis identified age older than 65 years, use of inotropic support, and ineffective initial therapy as independent risk factors of poor outcome.

CONCLUSIONS: The predominant pathogenic bacteria of aspiration pneumonia in patients admitted to an RICU were antibiotic-resistant bacteria, and effective initial supportive management secured better prognosis.

Curious Cases

Relevant links to my Medscape blog

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Last Update: 11/04/18.