Infectious Diseases I

Answer: D

The patient described has early onset VAP without

apparent updated risk factors for MDROs (Answers

A, B, and C, are incorrect). Pathogens associated with

early onset hospital-acquired pneumonia and VAP in

the absence of other MDR risk factors are usually com-

munity-acquired organisms, including S. pneumoniae,

MSSA, H. influenzae, and enteric gram-negative bacilli

(Answer D is correct). However, because some epide-

miological studies have documented the occurrence of

traditionally nosocomial or late-onset pathogens within

5 days from admission, guideline updates recommend

that P. aeruginosa coverage be considered as empiric

therapy for all patients suspected of having VAP. This

further emphasizes the importance of understanding

local VAP pathogen trends amid MDR risk factors and

time from admission to onset. Atypical bacteria are

rarely associated with early onset VAP. If MDRO risk

factors were present, MRSA and P. aeruginosa would

also be considered.

Empiric antibiotic choices for VAP should be based on

the likely causative pathogens, the presence of MDRO

risk factors, and local antibiotic susceptibility patterns.

The 2016 IDSA guidelines recommend P. aeruginosa

coverage as empiric therapy for all patients suspected

of having VAP, with monotherapy antipseudomonal

β-lactam sufficient in the absence of MDRO risk factors

or if the local antibiogram suggests less than 10% resis-

tance. Therefore, cefepime is preferred to ceftriaxone

(Answer B is correct; Answers C and D are incorrect).

Atypical bacteria are rarely associated with early-onset

VAP (Answer A is incorrect).

Answer: D

Gram-positive organisms are the most common cause of

CLABSI, including MRSE and MRSA. Vancomycin is

the best option listed for empiric management (Answer D

is correct). Although linezolid has a sufficient spectrum

of activity against these organisms, it is not recom-

mended for empiric management of CLABSI because

of concerns for worse patient outcomes (Answer B is

incorrect). The other options are inactive against MRSE

and MRSA and could be considered in addition to van-

comycin if there were a high suspicion for additional

pathogens (Answers A and C are incorrect).

Answer: D

Given the high prevalence of the 2009 H1N1 subtype of

influenza A, oseltamivir is the empiric drug of choice. In

addition, oseltamivir has high-level activity against other

contemporary influenza A and B subtypes (Answer D is

correct). Zanamivir also has high-level activity against

these strains; however, inhaled therapy through the

mechanical ventilator is not indicated because of insuf-

ficient systemic delivery, and intravenous zanamivir is

available through compassionate use and indicated only

if oseltamivir cannot be administered (e.g., patient is

unable to receive enteral medications, has poor absorp-

tion) (Answers B and C are incorrect). Amantadine has

insufficient activity against most contemporary influ-

enza A and B strains (Answer A is incorrect).

Answer: B

Although a health care–associated CAUTI is caused by

a more diverse spectrum of pathogens, E. coli is still the

most common pathogen and is responsible for around

30% of cases (Answer B is correct). The other pathogens

listed are also possible and should be considered when

choosing empiric antibiotic therapy in patients with a

suspected CAUTI (Answers A, C, and D are incorrect).

Answer: D

This patient has community-acquired complicated

intra-abdominal infection involving the middle small

intestine. Although enteric gram-negative bacilli (e.g.,

E. coli, Klebsiella spp.) are the most common pathogens

related to this type of infection, patients with severe dis-

ease, as evidenced by concomitant septic shock, are at

a higher risk of MDROs, including P. aeruginosa and

enterococci. Piperacillin/tazobactam has empiric activ-

ity against these organisms, whereas the other regimens/

agents listed have relevant gaps in the bacterial spec-

trum relative to these pathogens (Answer D is correct;

Answers A–C are incorrect).

Answer: A

This patient presents with severe acute pancreatitis with

radiographic evidence of pancreatic necrosis. Although

the patient presents with SIRS, the absence of signifi-

cant fluid collection or abscess suggests there is no

concomitant infection. As such, there is no indication

for empiric antibiotic therapy at this time (Answer A is

correct; Answer B is incorrect). Most recent evidence