A 63-year-old man presents to the physician complaining of fever and cough. One week ago, he developed fever, a nonproductive cough, and myalgias. He started to feel better after 3 days, but then the fever came back and his cough became productive of dark yellow sputum. He is now short of breath with any activity. His past medical history is negative for pulmonary disease, and he has never smoked tobacco. He has a fever of 39°C and is tachypneic. A chest x-ray shows pulmonary infiltrates.
Which of the following is likely to be seen on Gram stain of the expectorated sputum?
Gram-positive cocci in clusters. S. aureus pneumonia is commonly seen in patients recovering from influenza. Notice that lancet-shaped gram-positive diplococcus was not an answer choice, since this is actually the most common organism to cause postinfluenza pneumonia (S. aureus is the second most common). Both young and old patients recovering from influenza are at risk for secondary bacterial infection, since the primary infection and surrounding inflammation causes cellular damage leading to loss of cilia and other defense mechanisms. Therefore, if S. aureus pneumonia is suspected based on the history of a preceding viral infection, empiric antibiotics should include coverage of MRSA until more information is obtained from Gram stain and culture.
The following important organisms match the description on Gram stain: (B) Clostridium (“box-shaped”), Listeria (variable shapes), Nocardia (“branching”), Corynebacterium (“Chinese letters”); (C) Streptococcus pyogenes (group A strep), Enterococcus, Peptostreptococcus; (D) Moraxella catarrhalis (diplococcus), Haemophilus influenzae (coccobacillus); (E) Pseudomonas, Klebsiella, E. coli, Enterobacter, Serratia marcescens, Acinetobacter (pleomorphic); Some organisms are not visualized by Gram stains (e.g., Mycoplasma, Chlamydophila).
A 62-year-old man presents with fever, headache, and nuchal rigidity. His mental status is intact, and he has not experienced any seizures. He is admitted to the hospital with a presumptive diagnosis of meningitis, and a lumbar puncture is performed and shows slightly cloudy CSF without significant blood or xanthochromia. Screening blood laboratory values and CSF studies are pending.
What antibiotics should be started at this time?
Ceftriaxone, vancomycin, and ampicillin. Since blood and CSF cultures may take days to provide the identity of the causative organism as well as information about antibiotic sensitivities, it is important to have an understanding of common organisms and the empiric antibiotics that will cover them. The most common cause of bacterial meningitis is S. pneumoniae, which is often resistant to penicillin. Therefore, empiric antibiotic regimens typically include ceftriaxone, which has activity against most strains of S. pneumoniae. However, there are strains of S. pneumoniae that are resistant to third-generation cephalosporins, and therefore vancomycin is added to the regimen to cover these resistant strains. (A) In children, alcoholics, and older patients (>50 years old), Listeria is a potential pathogen and therefore ampicillin should be added to the regimen.
(B) Acyclovir is used empirically in cases of suspected HSV encephalitis, which will often present with RBCs in the CSF and mental status changes. (Note: Xanthochromia refers to yellowish discoloration of the CSF caused by metabolized heme, which can be seen in subarachnoid hemorrhage.)
(D) Dexamethasone has shown a benefit in patients with meningitis due to S. pneumoniae; the greatest benefit is giving this to patients with a depressed mental status and with the first dose of empiric antibiotics (before culture data). This would be an appropriate answer choice if it included ampicillin in the regimen. (E) In patients who are immunosuppressed, a good regimen includes vancomycin, ceftazidime, ampicillin, and acyclovir.
Another point to consider is that antibiotic prophylaxis should be given to close contacts of patients with meningitis due to N. meningitidis. Options include rifampin, ciprofloxacin, or ceftriaxone. Rifampin is also the prophylactic antibiotic of choice for close contacts of H. influenzae.
A 36-year-old woman presents to her physician worried that she is pregnant. She is married and has been sexually active with her husband, and they normally use condoms for contraception. However, his condom broke during intercourse and she is now worried that she will become pregnant. She has urine studies performed, which show a negative pregnancy test and growth of E. coli from a clean-catch specimen. Two weeks later, she follows up for repeat testing, which give the same results. She denies any fevers, chills, flank pain, dysuria, hematuria, urgency, or frequency.
What should be done next in the management of this patient?
: Reassurance. This patient has asymptomatic bacteriuria, defined as two clean-catch urine specimens that grow ≥105 colony forming units per mL. Only pregnant patients and those undergoing significant urologic procedures need to be treated with antibiotics. (A) This is a treatment option for inpatient management of pyelonephritis. (B) This is one of the standard treatments for cystitis, with other empiric options including nitrofurantoin and trimethoprim-sulfamethoxazole. (C) The urine pregnancy test reacts to urinary β-hCG, and serum levels do not need to be measured. Situations in which it is useful to measure serum β-hCG include ectopic pregnancy and gestational trophoblastic disease.
A 31-year-old woman presents to an obstetrician for prenatal care. She is 12 weeks pregnant based on her last menstrual period, and has been taking her prenatal vitamins during this time. She has been pregnant twice before, and both pregnancies resulted in miscarriages. Her medical history is significant for hypertension and a previous deep venous thrombosis. She takes no other medications and is allergic to penicillin and cephalexin. As part of a routine workup, she is tested for syphilis and HIV. Serologic testing for HIV is negative, and her rapid plasma reagin (RPR) is reactive.
What is the most appropriate next step in management?
Testing for fluorescent treponemal antibody absorption (FTA-ABS) reactivity and screening for autoantibodies. There is a high rate of both false positives and false negatives with both nontreponemal (e.g., RPR, VDRL) and treponemal tests (e.g., FTA-ABS) for syphilis. One commonly tested cause of a false-positive test is SLE, especially the antiphospholipid syndrome. This patient’s history is concerning for the antiphospholipid syndrome given her history of multiple miscarriages and a thrombotic event. False-positive syphilis tests occur due to cross-reactivity with antiphospholipid antibodies (anticardiolipin, anti–β2-glycoprotein I, or lupus anticoagulant); a reactive nontreponemal test followed by a nonreactive treponemal test indicates a false-positive test. The patient should also be screened for SLE and antiphospholipid antibodies, given the suspicion for one of these diagnoses. (B, D, E) If this patient were to have syphilis, she should be desensitized to penicillin since she has a penicillin allergy and then treated immediately with penicillin, since this is the only therapy shown to be safe and effective during pregnancy. (C) In nonpregnant patients, other antibiotic options (e.g., doxycycline, azithromycin) are available for the treatment of syphilis; however, doxycycline is teratogenic.
An important cause of a false-negative syphilis test is the prozone reaction. This occurs in cases where there are high levels of serum antibodies (e.g., secondary syphilis) that interfere with agglutination. The specimen must be diluted for agglutination to occur and cause a positive result.
A 45-year-old woman with a history of HIV presents to the hospital with worsening confusion, headache, and fever. She has not been to her physician for follow-up in years, and has not been compliant with her medications. She has been hospitalized twice in the past year for pneumonia. Her last CD4 count measured 6 months ago was 140/mm3 . She is admitted and found to be febrile to 38.6°C. She appears lethargic and vomits several times. Her CD4 count is measured again during this hospitalization and is found to be 76/mm3 . An MRI is performed, and the postcontrast T1-weighted image is shown below.
Which of the following could have prevented this from happening?
Trimethoprim-sulfamethoxazole prophylaxis. Encephalitis is the most common manifestation of Toxoplasma gondii, and this organism may reactivate to form CNS abscesses when the CD4 count drops below 100 mm3 . Suspect this diagnosis in HIV patients who are not taking prophylactic antibiotics and who have multiple ring-enhancing lesions on brain imaging. The acute treatment is pyrimethamine-sulfadiazine, and patients should receive trimethoprim-sulfamethoxazole prophylaxis until they have sufficient immune reconstitution on antiretroviral medications. Other important cutoffs to remember for antibiotic prophylaxis of opportunistic infections are trimethoprim-sulfamethoxazole for PCP prevention when the CD4 count is <200/mm3 , and azithromycin for mycobacterium avium complex (MAC) prevention when the CD4 count is <50/mm3 . If the CD4 count rises above these thresholds for >3 to 6 months after antiretrovirals are started, antibiotic prophylaxis can be stopped.
(A) This patient’s CD4 count is >50/mm3 , so azithromycin should not be started prophylactically. (B) HIV patients are at an increased risk of multiple cancers, including CNS lymphoma. As opposed to multiple ring-enhancing lesions on brain imaging with toxoplasmosis, CNS lymphoma will typically present as a solitary lesion that may ring-enhance, although whole tumor enhancement is more common. Also look for a positive PCR test for EBV in a CSF sample. (E) Another important item on the differential diagnosis is progressive multifocal leukoencephalopathy (PML) due to polyomavirus JC (JC virus), which presents with multiple lesions that do not ring-enhance. It has a very poor prognosis and there is no treatment or specific preventive strategies other than antiretrovirals. (D) This is the treatment for latent TB, which may cause meningitis. Patients with HIV should be screened for latent TB, but there is no prophylactic treatment that is currently recommended to prevent TB infection.
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