Chapter 8-02: Approaches & Chief Complaints in Infectious Diseases

Define the illness

Host:

• Different individuals, depending on their age, exposure history, prior infections, and immune status, are at risk for different types of infections.

• An understanding of the host allows us to better understand the organisms to which they are most susceptible.

Tempo:

• Different pathogens cause different tempos of illness. Labeling the illness tempo will help us determine with more precision which infections are more or less likely.

• Generally, we can label the time course as acute (from hours/days to 1 week), subacute (weeks to months), and chronic (months to years).

Clinical syndrome:

• Define the clinical syndrome (e.g., pneumonia or cholangitis).

Putting it together:

• The first step in a suspected infection is to frame the patient based on these three features, for example:

  • - An individual with HIV and a CD4 112 cells/μL presents with subacute onset of fever and cough.

  • - An elderly person with hypertension presents with acute onset fever and cough.

• While these two individuals have a similar clinical syndrome, the potential organisms that cause this syndrome vary based on the host (individual with HIV vs. elderly immunocompetent person) and tempo (weeks vs. days).

Select an empiric therapy

• Many infections have a high morbidity and mortality early in the course of illness when there is still diagnostic ambiguity. Therefore, we often start antimicrobial therapy prior to identifying the definitive pathogen(s). Most suspected infections that require hospitalization warrant empiric antibiotic therapy.

• Based on the host, tempo, and clinical syndrome, generate a list of possible and probable pathogens, which guides empiric antibiotic therapy.

• See Table 8.12 for empiric antibiotic regimens for commonly encountered infections.

Finalize the management plan

Targeted antibiotics and duration of therapy:

• Targeted antibiotics depend on the antimicrobial susceptibilities of the identified organism(s)

• The duration of therapy depends on the type of infection

Source control: Source control is a key step in controlling any infection. Niduses for ongoing infection include:

• Indwelling catheters

• Infected fluid pockets (e.g., an abscess or effusion)

• Obstructed organs (e.g., pyelonephritis with an obstructing stone or cholangitis)

Meningitis (community onset, age <50 yr and no immunocompromising condition)

Bacteria:

• Streptococcus pneumoniae

• Neisseria meningitidis

• Group B Streptococcus

• Hemophilus influenzae

Viruses:

• HSV1

• VZV

• vancomycin

• ceftriaxone (2 g IV q12hr)

• +/– acyclovir (if HSV encephalitis is suspected)

• +/– adjunctive corticosteroids (dexamethasone 0.15 mg/kg q6hr)

• Perform a lumbar puncture (LP) to confirm the diagnosis

• Do not delay empiric antibiotics if the LP is delayed

• Immunocompromising conditions include HIV, solid organ or bone marrow ...