COMSA Review Qbank

The classic teaching is that typical organisms (Streptococcus pneumoniae, Klebsiella, Haemophilus influenzae) produce focal lobar consolidation with air bronchograms while atypical organisms (Mycoplasma, Chlamydophila, viruses) produce diffuse patchy interstitial infiltrates with findings that look worse than the patient does. In practice this correlation is unreliable: Mycoplasma can consolidate and pneumococcus can look patchy, and guidelines base empiric therapy on the site of care and comorbidities rather than the radiographic pattern. That is why the first two options and the claim about air bronchograms are wrong. A radiograph can also be falsely negative early or in dehydration, so a normal film does not exclude pneumonia.

Amoxicillin covers typical organisms only, with the best pneumococcal activity and the narrowest spectrum, and it has no activity against cell-wall-deficient Mycoplasma or intracellular Chlamydophila. Macrolides (azithromycin), tetracyclines (doxycycline), and respiratory fluoroquinolones (levofloxacin, moxifloxacin) all cover both typical and atypical pathogens, which is exactly why a single agent can be given empirically without identifying the organism. Note that amoxicillin monotherapy is an accepted outpatient option specifically for otherwise healthy adults without comorbidities, as here; patients with comorbidities require a beta-lactam plus a macrolide or doxycycline, or a respiratory fluoroquinolone alone.

Macrolides do cover S. pneumoniae, which is why macrolide monotherapy remains an option for healthy outpatients with no comorbidities. The limiting factor is resistance: pneumococcal macrolide resistance runs roughly 25 to 30 percent in much of the United States, so guidelines restrict monotherapy to areas with local resistance below 25 percent, and many clinicians now default to amoxicillin or doxycycline instead. "Macrolides have no meaningful activity against Streptococ..." is wrong because macrolides are active against susceptible pneumococcus. "The only gap in macrolide monotherapy is the absence of a..." inverts the pharmacology: macrolides are the classic atypical drugs (Mycoplasma, Chlamydophila, Legionella); the gap is resistant pneumococcus. "Pneumococcal macrolide resistance is beta-lactamase mediated" is wrong because macrolide resistance is by ribosomal methylation (erm) and efflux (mef), not beta-lactamase, so a beta-lactamase inhibitor does nothing. "Pneumococcal macrolide resistance is under 5 percent nati..." misstates the epidemiology, which is exactly why the 25 percent threshold exists.

For a healthy outpatient with community-acquired pneumonia and no drug allergy, high-dose amoxicillin is first-line: it has the best activity against Streptococcus pneumoniae (the most common pathogen) and the narrowest spectrum. A documented penicillin allergy is what removes amoxicillin and moves you to a macrolide or doxycycline, which happen to also cover atypicals. "Azithromycin 500 mg orally on day 1, then 250 mg daily" is the allergy or resistance-driven alternative, not the preferred agent in a patient who can take a penicillin. "Levofloxacin 750 mg orally daily" reserves too much: respiratory fluoroquinolones are for patients with comorbidities, recent antibiotics, or high local resistance, given tendon rupture, QT prolongation, "Levofloxacin 750 mg orally daily". difficile, and aortic aneurysm risk. "Ceftriaxone 1 g intravenously daily plus azithromycin" is inpatient-level therapy in a patient who is hemodynamically stable and well oxygenated. "Amoxicillin-clavulanate 875/125 mg orally twice daily" adds unnecessary beta-lactamase and anaerobic coverage with more GI toxicity and no benefit against pneumococcus.

"Opacity" is deliberately non-specific: it says an area is denser than expected without committing to a mechanism, so it covers consolidation, atelectasis, pleural effusion, or mass. "Consolidation" is the specific term for alveolar filling (air spaces replaced by fluid, pus, blood, or cells), often with air bronchograms. "It is synonymous with consolidation and confirms an alveo..." and "It establishes lobar pneumonia and obviates the need for..." overread the word: you cannot infer a lobar alveolar process from "opacity" alone. "It specifically indicates interstitial rather than alveol..." is wrong because opacity does not distinguish interstitial from alveolar patterns; that requires a qualifier such as reticular or nodular. "It indicates increased lucency" reverses the meaning; increased lucency is the opposite of opacity.

The right mainstem bronchus is wider, shorter, and takes a more vertical course off the carina than the left, so inhaled particles, aspirated material, and even malpositioned endotracheal tubes preferentially go right, and gravity then directs material to the lower lobe. The clinically important corollary: because the right lower lobe is the most common site of pneumonia of ANY cause, right lower lobe location by itself does NOT distinguish aspiration from ordinary community-acquired pneumonia. You need a risk factor for that. "The right lower lobe receives a greater share of bronchia..." is wrong because the bronchial circulation does not drive this distribution. "The left lower lobe is protected by the cardiac notch" invents a mechanism; the cardiac notch is a feature of the left upper lobe and does not deflect aspirate. "Mucociliary clearance is absent in the right lower lobe" is false; mucociliary clearance is present throughout the conducting airways. "The right lower lobe has the lowest ventilation-to-perfus..." misuses physiology: lung bases have a LOWER ventilation-to-perfusion ratio than apices, but that is a gas exchange phenomenon and not the reason for pneumonia location.

Aspiration follows gravity in whatever position the patient was in. Supine aspiration drains into the SUPERIOR segment of the right lower lobe or the POSTERIOR segment of the right upper lobe, because those are the most dependent segments when a patient lies on the back. "Basal segments of the right lower lobe" is the answer for aspiration in the UPRIGHT position, when basal segments of the right lower lobe are dependent, and this patient was found supine. "Lingula of the left upper lobe" and "Superior segment of the left lower lobe" are left-sided and less favored because the right mainstem bronchus is wider, shorter, and more vertical. "Anterior segment of the right upper lobe" is wrong on position: the ANTERIOR segment of the right upper lobe is non-dependent when supine; it is the POSTERIOR segment of the right upper lobe that is at risk.

Aspiration is a clinical diagnosis anchored to a risk factor for impaired airway protection: altered consciousness, alcohol use disorder, stroke, dysphagia, seizure, dementia, recent intubation or extubation, tube feeds, poor dentition, and GERD. Post-stroke dysphagia with coughing during meals is exactly that. "The infiltrate is located in the right lower lobe" is the classic trap: the right lower lobe is the most common site for pneumonia of any cause because of right mainstem bronchial anatomy, so lobe alone never establishes aspiration. "He completed a stay at a hotel with a large recirculating..." points to Legionella (water systems, air conditioning, cruise ships). "He had influenza A confirmed 6 days before symptom onset" points to post-influenza Staphylococcus aureus, which is often necrotizing or cavitary. "His sputum is described as rusty" is the rusty sputum of Streptococcus pneumoniae, not aspiration.

Klebsiella pneumoniae produces thick, blood-tinged "currant jelly" sputum and is classic in alcohol use disorder, diabetes, and aspiration. It characteristically causes UPPER lobe cavitation and a BULGING FISSURE, because the volume of the inflammatory exudate physically displaces the fissure. "Streptococcus pneumoniae" causes rusty (not currant jelly) sputum with lobar consolidation, and cavitation is uncommon. "Mycoplasma pneumoniae" causes patchy bilateral infiltrates in a young adult with a gradual, prodromal course and does not cavitate. "Legionella pneumophila" presents with high fever, diarrhea, confusion, and hyponatremia rather than currant jelly sputum. "Pseudomonas aeruginosa" cavitates but occurs in bronchiectasis, cystic fibrosis, neutropenia, or ventilated patients, not in this host profile.

Third-generation cephalosporins such as ceftriaxone do cover susceptible Klebsiella, but there are two caveats. First, they have NO anaerobic activity, so aspiration requires added metronidazole or a switch to ampicillin-sulbactam. Second, ESBL-producing strains hydrolyze third-generation cephalosporins, and the reliable therapy for a serious ESBL infection is a CARBAPENEM such as meropenem. "Increase the ceftriaxone dose and continue" fails because enzymatic hydrolysis is not overcome by raising the dose. "Change to cefepime monotherapy" is unreliable: cefepime is also hydrolyzed by ESBLs and is inferior to carbapenems for invasive ESBL infection. "Change to ceftazidime" is another cephalosporin subject to the same ESBL hydrolysis; its distinguishing feature is antipseudomonal activity, which is irrelevant here. "Add azithromycin to the ceftriaxone" adds atypical coverage that does nothing against a gram-negative ESBL producer.

Ceftazidime is the third-generation cephalosporin with antipseudomonal activity, at the cost of weaker gram-positive coverage. "Ceftriaxone" and "Cefotaxime" are the other common third-generation agents, and neither ceftriaxone nor cefotaxime has any meaningful antipseudomonal activity. "Cefuroxime" is second generation and not antipseudomonal. "Cefazolin" is first generation, aimed at streptococci and methicillin-susceptible Staphylococcus aureus, with no Pseudomonas coverage. (Cefepime, a fourth-generation agent, is also antipseudomonal, but the question asks specifically about third generation.)

Reliable anaerobic coverage comes from ampicillin-sulbactam, piperacillin-tazobactam, amoxicillin-clavulanate, metronidazole, clindamycin, carbapenems, and moxifloxacin. Ampicillin-sulbactam is the standard single-agent choice for aspiration pneumonia, since the sulbactam covers oral anaerobes along with the usual respiratory flora. "Ceftriaxone" is a common trap: ceftriaxone has NO anaerobic coverage, so it must be paired with metronidazole for aspiration. "Azithromycin" has no reliable anaerobic activity. "Levofloxacin" is the fluoroquinolone trap: levofloxacin does NOT reliably cover anaerobes, whereas moxifloxacin does, and this is the classic point of discrimination between the two respiratory quinolones. "Ceftazidime" likewise lacks anaerobic coverage; ceftazidime is chosen for Pseudomonas.

This is Mycoplasma pneumoniae, or walking pneumonia: a young patient, gradual onset with a viral-type prodrome, prominent myalgia, patchy bilateral infiltrates, and radiographic findings out of proportion to how well the patient appears. Treat with a macrolide such as azithromycin, or with doxycycline. "Amoxicillin", "Cefuroxime", "Ampicillin-sulbactam", and "Nafcillin" are all beta-lactams, and every one of them FAILS here for the same reason: Mycoplasma has no cell wall, so there is no peptidoglycan target for a beta-lactam to attack. That single mechanistic fact is the discriminating point.

Two classic extrapulmonary findings of Mycoplasma pneumoniae are cold agglutinin autoimmune hemolytic anemia (IgM-mediated, complement-positive on direct antiglobulin testing) and bullous myringitis, the blebs seen on the tympanic membrane. Mycoplasma is also a well-known trigger of erythema multiforme and Stevens-Johnson syndrome. "Legionella pneumophila" causes hyponatremia, diarrhea, confusion, and elevated LFTs, not cold agglutinin hemolysis or myringitis. "Klebsiella pneumoniae" causes currant jelly sputum with upper lobe cavitation and a bulging fissure. "Streptococcus pneumoniae" causes rusty sputum and lobar consolidation. "Staphylococcus aureus" causes post-influenza necrotizing or cavitary pneumonia.

High fever, diarrhea, confusion, hyponatremia, and elevated LFTs in a patient exposed to a contaminated water system (cruise ships, air conditioning, cooling towers, hotel plumbing) is Legionella pneumophila. The rapid confirmatory test is the URINARY ANTIGEN test (which detects serogroup 1, the dominant clinical serogroup), and treatment is a macrolide or a respiratory fluoroquinolone. "Cold agglutinin titer" tests for Mycoplasma-associated cold agglutinins, which do not fit hyponatremia and diarrhea. "Sputum acid-fast bacilli smear" targets tuberculosis, which would present with weeks of weight loss, night sweats, and upper lobe cavitation. "Serum cryptococcal antigen" screens for cryptococcosis, a concern in advanced immunosuppression. "Nasopharyngeal swab for influenza PCR" is reasonable in influenza season, but influenza does not explain hyponatremia with transaminitis and diarrhea, and it would not be the most appropriate test given this specific syndrome.

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia and gives the classic picture here: abrupt onset with rigors, high fever, pleuritic pain, RUSTY sputum (blood mixed with purulent secretions), and lobar consolidation with air bronchograms. "Mycoplasma pneumoniae" has a gradual onset with patchy bilateral infiltrates in a younger patient. "Klebsiella pneumoniae" produces currant jelly sputum with upper lobe cavitation and a bulging fissure in patients with alcohol use disorder or diabetes. "Legionella pneumophila" presents with diarrhea, confusion, and hyponatremia. "Haemophilus influenzae" is a real cause of CAP, especially in COPD and smokers, but it does not carry the rusty sputum and abrupt rigors signature and is far less common overall.

Post-influenza pneumonia that is necrotizing or cavitary, especially with a biphasic course (initial improvement then abrupt deterioration), is Staphylococcus aureus, including MRSA. Recent influenza is one of the specific risk factors that triggers empiric MRSA coverage in community-acquired pneumonia, alongside prior MRSA isolation, recent hospitalization with IV antibiotics, and empyema. "Mycoplasma pneumoniae, so add azithromycin" is wrong because Mycoplasma does not cavitate and does not cause this fulminant post-influenza course. "Legionella pneumophila" is a plausible severe pneumonia but is not the post-influenza cavitary syndrome and lacks the hyponatremia, diarrhea, and confusion cluster. "Streptococcus pneumoniae, so continue ceftriaxone alone" ignores the cavitation, and pneumococcus rarely cavitates. "Pneumocystis jirovecii" is a subacute hypoxemic pneumonia in advanced immunosuppression with diffuse ground-glass rather than cavities.

Penicillin allergy is what removes amoxicillin and moves a healthy outpatient to a macrolide or doxycycline, both of which also cover atypicals. "Levofloxacin" is reserved, not first-line: respiratory fluoroquinolones are held for patients with comorbidities, recent antibiotic exposure, or high local macrolide resistance, because of tendon rupture, QT prolongation, "Cefuroxime". difficile, and aortic aneurysm or dissection risk. "Cefuroxime" is a beta-lactam and is avoided after documented anaphylaxis to a penicillin, and it also lacks atypical coverage. "Amoxicillin-clavulanate" contains amoxicillin and is directly contraindicated. "Trimethoprim-sulfamethoxazole" has unreliable pneumococcal and atypical activity and is not a community-acquired pneumonia regimen.

Cross-reactivity tracks the R1 side chain, not the shared beta-lactam ring. First-generation agents (cefazolin is actually the exception, with a unique side chain) and cephalexin share side chains with penicillins and cross-react more; third-generation agents such as ceftriaxone and cefpodoxime have dissimilar side chains, with reaction rates around 1 to 3 percent or lower. "Cross-reactivity is driven by the shared beta-lactam ring" is the classic outdated 10 percent figure derived from studies contaminated with penicillin residue. "Cross-reactivity increases with each successive cephalosp..." inverts reality: later generations are less similar to penicillin, not more. "Cross-reactivity is essentially 100 percent" overstates the risk, and a benign delayed maculopapular rash is not even an IgE-mediated allergy. "Cross-reactivity is mediated by IgG rather than IgE" is wrong: immediate cephalosporin reactions are IgE-mediated and skin testing plus graded challenge is useful.

Neuraminidase inhibitors shorten illness only when started within about 48 hours of symptom onset; at 3 weeks the antiviral window has long closed. More importantly, a dense focal lobar consolidation with high fever after an influenza prodrome is post-influenza bacterial pneumonia (Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae), which needs antibiotics. "Oseltamivir is only active against influenza B" is false: oseltamivir covers influenza A and B. "Oseltamivir is contraindicated once a chest radiograph sh..." is invented; oseltamivir does not cause bronchospasm (inhaled zanamivir is the agent avoided in asthma and COPD). "Oseltamivir requires a negative procalcitonin before it m..." is not a rule. "Oseltamivir has no oral bioavailability and this patient..." is wrong: oseltamivir is an oral drug with good bioavailability (peramivir is the intravenous option).

Aminoglycosides miss the organisms that actually cause community-acquired pneumonia (pneumococcus, atypicals), penetrate lung parenchyma and purulent, acidic, low-oxygen environments poorly, must be given parenterally, and require peak/trough monitoring because of nephrotoxicity and ototoxicity. None of that fits an ambulatory patient. "They are inactivated by gastric acid but otherwise have i..." is wrong in emphasis: they are indeed not absorbed orally, but the fatal flaw is spectrum and lung penetration, not the route alone. "They induce a high rate of Clostridioides difficile colit..." is backwards: aminoglycosides are among the lower-risk classes for "They induce a high rate of Clostridioides difficile colit...". difficile (clindamycin, fluoroquinolones, and cephalosporins are the classic offenders). "They select rapidly for extended-spectrum beta-lactamase..." describes cephalosporin pressure, not aminoglycosides. "They antagonize the activity of any beta-lactam given wit..." is the opposite of the truth: beta-lactams and aminoglycosides are classically synergistic (the beta-lactam breaks the cell wall and increases aminoglycoside uptake).

Sympathetic innervation to the lungs arises from T2 to T7, so viscerosomatic reflex findings from pulmonary disease appear in that upper thoracic segment band (upper lung fields roughly T2 to T4, lower fields T5 to T7). "T5 to T9, sympathetic" is the sympathetic range for the stomach and upper gastrointestinal tract. "T10 to L2, sympathetic" corresponds to the kidney, ureter, and gonads. "OA, AA, and C2, sympathetic" names the cranial and upper cervical region, which is where vagal (parasympathetic) influence on the lungs is addressed, and those levels are parasympathetic, not sympathetic. "T2 to T7, parasympathetic" has the correct levels but the wrong division: parasympathetic supply to the lungs is the vagus nerve, treated at the OA, AA, and C2 region, not at T2 to T7.

Smoking and COPD damage mucociliary clearance and predispose to Haemophilus influenzae and Moraxella catarrhalis in addition to pneumococcus. Both organisms commonly produce beta-lactamase, so a beta-lactamase inhibitor combination (amoxicillin-clavulanate) is chosen over plain amoxicillin. "Pseudomonas aeruginosa and Stenotrophomonas maltophilia" applies to advanced structural lung disease such as bronchiectasis, cystic fibrosis, or frequent steroid and antibiotic exposure, not to uncomplicated COPD. "Klebsiella pneumoniae and anaerobes" describes aspiration in a patient with poor dentition or alcohol use disorder. "Legionella pneumophila and Mycoplasma pneumoniae" lists atypicals, which are not specifically increased by COPD, and azithromycin monotherapy would be inadequate for a patient with significant comorbidity. "Staphylococcus aureus and Streptococcus pyogenes" describes post-influenza or necrotizing pneumonia, not the COPD pattern.