Approach to Clinical Syndromes: Part I

Taking an ID History

An ID history is mostly like any internal medicine history, with a few areas where we go into greater detail.

Identifying information
Past medical history: include any relevant infections, as well, such as MSSA bacteremia or ESBL UTIs
Allergies: for antibiotic allergies, get into the details of when and what
Antimicrobials: a timeline of recent antibiotics, antifungals, and antivirals, including their current doses
Medications: make sure to highlight any immunosupression
Social history: can be an important source of risk factors, but I sometimes put some of it in a separate "Exposure history" section
Family history: rarely relevant
History of presenting illness: a timeline of events from when they first developed symptoms, including antibiotic exposures
Review of systems: as usual, it should be focused on making a diagnosis, but also screening for side effects of any antibiotics that they've been on (most commonly, nausea and diarrhea)
Exposure history: if it's an unusual case, I usually have a completely separate section dedicated to listing every possible exposure that they've had. This includes travel (listing essentially each city they've visited in a timeline, with any activities or exposures there), animal and insect exposures, food exposures, freshwater or saltwater exposures, injection drug use, TB risk factors, and anything else you can think of.
Physical exam
Microbiology: a section that is separate from the investigations, which lists all of their recent (or remote, if relevant) microbiology results
Investigations
Impression and plan

When presenting the case, it takes the same order as above, but you don't need to present everything. The past medical history up to social history should be short. Only mention things that are relevant to their current complaint, as well as any significant previous infections. Make sure to mention any antibiotic allergies. We usually only care about medications that are immunosuppressing (like prednisone) or that will interact with antimicrobials.

The history of presenting illness is the main part of the presentation, where you should try to tell a narrative that weaves together their microbiology and antimicrobials. For example, you might say, "Mr. B presented with one week of cough and dyspnea. He was hypoxic in the ED and required intubation. He was started empirically on ceftriaxone for pneumonia, then when his sputum came back with Pseudomonas he was switched to pip/tazo. Sensitivities are still pending." Although you will document the microbiology and antimicrobial history separately in your note, you won't present them except in the context of the HPI.

Choosing an Empiric Antibiotic

Is there an infection? If not, no antibiotics are needed. This can be a more difficult question to answer than many people think. And, since there is often clinical uncertainty about this, we often treat for possible infections regardless, while waiting for more information.
What is the clinical syndrome? By this I mean do they have a community-acquired pneumonia, a urinary tract infection with fever (i.e. pyelonephritis), an intraabdominal abscess, a diabetic foot infection, etc. Each syndrome has a different set of things to worry about, and we will discuss each of the common syndromes in turn.
Which bacteria, in general, cause this syndrome? For each syndrome, there is a list of bacteria that can be ordered from most common to least common, and from most dangerous to least dangerous.
Which other bacteria do I have to worry about in this patient? Consider the patient themselves. Are they immunocompromised? Have they been in the ICU for the past five years? Did they just return from a month in India? Are they known to be colonized, or have they been previously infected by, resistant bacteria like MRSA, VRE, ESBLs, Pseudomonas, etc. Digging down into a patient's specific risk factors is one of the most important things that an ID doc does.
Which antibiotic(s) will treat the majority of bacteria listed above? If there are many options (and there always are), then pick the safest (which is usually a beta-lactam). Make sure to take a detailed history of any reported antibiotic allergies, since beta-lactams are usually the most effective and safest, and should be preferred unless there is a fairly clear history of allergy.