INFECTION/EXCLUSIVES:

INFECTION:

Q. The duration of treatment for infections caused by rapidly growing mycobacteria is usually?
A. 7 to 10 days
B. 10 to 14 days
C. 14 to 28 days
D. 1 to 3 months
E. 4 to 6 months

Ans: E.

As with TB therapy, treatment of rapidly growing mycobacterial infections usually is very prolonged. Most skin and soft tissue infections require a combination of debridement and long courses of therapy; pulmonary infections may require even more than 6 months of appropriate chemotherapy for cure.

Q. What biochemical feature of Salmonella distinguishes it from most of the enteric flora (other enterobacteraciae)?
A. Lactose nonfermenter
B. Glucose fermenter
C. Oxidase negative
D. Nitrate reducer
E. Failure to produce hydrogen sulfide

Ans: A.

 Enteric pathogens, such as Salmonella and Shigella, are often distinguished from normal fecal flora by using plates such as MacConkey agar or Hektoen agar, which allow easy selection of lactose nonfermenters. The enterobacteraciae and Salmonella are glucose fermenters, oxidase negative, and nitrate reducing (B–D). Salmonella does produce hydrogen sulfide, which distinguishes it from Shigella and most enterobacteraciae.

Q. Which of the following combination would be most appropriate for a serious P. aeruginosa pneumonia with bacteremia in a bone marrow transplant recipient?
A. Penicillin and gentamicin
B. Cefepime and tobramycin
C. Cefepime and piperacillin
D. Ciprofloxacin and cefuroxime
E. Imipenem and ticarcillin

Ans: B.

The combination of an appropriate β-lactam antibiotic and an aminoglycoside is the most effective combination against P. aeruginosa. Penicillin does not have activity against P. aeruginosa. Both (C) and (E) are incorrect answers because combinations of two β-lactam antibiotics, even if they both have activity against P. aeruginosa, are antagonistic. Cefuroxime in (D) is a secondgeneration cephalosporin without activity against the organism

Q. Which of the following is a risk factor for P. aeruginosa associated necrotizing enterocolitis?
A. Use of prior antibiotics
B. Mesenteric ischemia
C. Neutropenia
D. Ulcerative colitis
E. Pseudomembranous colitis

Ans: C.

Neutropenia in cancer patients is a risk factor for necrotizing enterocolitis. The syndrome can also occur in young infants and is often fatal.

Q. Which of the following organisms, if found on a sputum culture, definitely indicates infection?

A. Chlamydia pneumoniae

B. Pneumococcus

C. Haemophilus influenzae

D. Legionella pneumophila

E. Moraxella

Ans: D.

Legionella is not known to be a colonizer; if it is found on culture, it should be treated. While Mycoplasma and Chlamydia cultures are rarely sent, these organisms can be found in  asymptomatic  subjects, so their mere presence does not require treatment. Moraxella, Haemophilus, and Pneumococcus can also be colonizers in asymptomatic patients. However, they should be treated in a patient with clinical signs of pneumonia and one of these organisms

predominating in a sputum Gram stain and culture.

Q. Which of the following host factors is most strongly linked to increased morbidity and mortality of WNV encephalitis?

A. HIV

B. Diabetes mellitus

C. Iatrogenic immunosuppression

D. Older age

E. Young age

Ans: D.

Convincing epidemiologic evidence, especially from the 1999 New York outbreak, shows that older age is a risk factor for death from WNV infection, as is an increased incidence of chronic neurologic sequelae.

Q. When should a patient with syphilis be treated with a drug other than penicillin?
A. Pregnancy
B. Penicillin-resistant syphilis is suspected
C. Neurosyphilis
D. Patient has a penicillin allergy
E. Topical treatment of syphilitic chancre in primary syphilis

Ans: D.

Syphilis is one of the very few pathogens in which drug resistance has not become a clinical problem. It is still exquisitely sensitive to penicillin. The only reason not to use penicillin is if

the patient has a severe allergy to the drug. Primary syphilis is a systemic infection and topical treatment is not possible. Neurosyphilis is still treated with penicillin, although the antibiotic

is given via continuous IV to achieve higher CNS levels. Penicillin is the only drug approved for use in pregnant patients.

Q. Which HIV drug is also active against HBV?

A. ddI

B. Indinavir

C. AZT

D. 3TC (lamivudine)

E. Nevirapine

Ans:  D.

Lamivudine is active against both HBV and HIV, as is tenofovir. Adefovir is also active against both viruses, but nephrotoxicity prevents adefovir from being used at the higher HIV dose.These

drugs have activity against HBV because HBV replication includes a reverse transcriptase step. Other HIV drugs, including the rest of the nucleoside analogs like AZT and ddI, are not active against HBV.

Q. Which enzyme is inhibited by zanamivir?

A. Reverse transcriptase

B. Hemagglutinin

C. Protease

D. Neuraminidase

E. Dihydrofolate reductase

Ans:   D.

 Zanamivir and oseltamivir are both neuraminidase inhibitors. Hemagglutinin (B) is the other major surface protein of influenza virus, used for binding to target cells. No drugs currently target it. Protease and reverse transcriptase (C and A, respectively) are drug targets in HIV. Dihydrofolate reductase (E) is inhibited by sulfa drugs and is a target in bacteria and parasites.

Q. Which of the following is a contraindication to influenza vaccination?

A. AIDS

B. Receipt of the vaccine within the previous 5 years

C. Pregnancy

D. Allergy to eggs

E. Severe pulmonary or cardiac disease

Ans: D.

Allergy to eggs is a contraindication to the vaccine because eggs are used to grow the virus for vaccine production. Becauseinfluenza virus is a killed virus, it is safe for AIDS patients (A)

and pregnant women (C) to receive. Patients with severe pulmonary or cardiac disease (E) benefit the most from vaccination because they are the most likely to die from influenza, and vaccination programs should target them. Whereas the Pneumovax should not be repeated more than every 5 to 7 years (D), the influenza vaccination needs to be given every year to maximize

protection against currently circulating virus.

Q. Which of the following drugs is active against influenza B?

A. Amantadine

B. Stavudine

C. Oseltamivir

D. Nelfinavir

E. Rimantadine

Ans:  C.

Oseltamivir (and zanamivir) are neuraminidase inhibitors active against both influenza A and B. Amantadine (A) and rimantadine (E) are both only active against influenza A. Stavudine (B)

is a nucleoside reverse transcriptase inhibitor active against HIV. Nelfinavir (D) is a protease inhibitor active against HIV.

Q. Mucormycosis can be distinguished from aspergillosis in that Mucor branches at angles of:

A. 15°

B. 30°

C. 60°

D. 90°

E. 150°

Ans: D.

Mucor and Rhizopus form nonseptate, true hyphae with broad irregular walls and branches that form at right angles (90º).

Q.A physician is obligated to treat yeast grown from which culture site?

A. Stool

B. Sputum

C. Skin

D. Urine

E. Blood

Ans: E. Blood cultures growing yeast could theoretically be contaminants, but the physician is obligated to treat them.Yeast can colonize the other listed sites without causing disease, although yeast skin and UTIs are often diagnosed and treated. True yeast pneumonias are exceedingly rare; usually yeast in the sputum is a colonizer of the oropharynx.

Q. Which of the following drugs acts by blocking yeast cell wall synthesis?

A. Amphotericin B

B. Penicillin

C. Fluconazole

D. Nystatin

E. Caspofungin

Ans: E.

Caspofungin, an echinocandin, blocks beta-glycan synthesis required to make yeast cell walls. This is analogous to the antibacterial antibiotic penicillin (B). Polyenes, such as amphotericin and nystatin (A and D, respectively), and azoles, such as fluconazole (C), target ergosterol, a component of the yeast cell membrane