HIV and ID Observations

Just finished two weeks on the inpatient general medical service — hence the radio silence — giving me a chance to work with residents, interns, and medical students. Here’s a smattering of the ID topics we discussed, along with a comment or two:

• “Common” causes of gram negative soft tissue infection (at least for board exam purposes), and their associations:  Pasturella multocida (cat bites), Vibrio vulnificus (salt water, especially in warmer climates), Aeromonas hydrophila (fresh water and leeches). Yes, leeches, which do have some legitimate medical indications. Our patient had Enterobacter cloacae (not leech-related), which led to a discussion about …
• “Inducible” AmpC beta lactamases, which get expressed after in vivo exposure to cephalosporins or expanded-spectrum penicillins. These are really tricky since the microbiology lab will report enterobacter spp. as sensitive to these antibiotics unless another resistance mechanism is present. So should all patients with serious infections due to enterobacter receive a carbapenem? Probably a good idea.
• Parasites are thought frequently to cause eosinophilia, but protozoan (single cell) parasites rarely do — except for the uncommon bugs Isospora belli, Dientamoeba fragilis, and Cyclospora cayetanensis. So if your patient has parasite-related eosinophilia, think worms — strongyloides, schistosomiasis, filariasis, etc.
• Is obsessive tweaking of vancomycin levels useful if you’re not treating confirmed Staph aureus and the patient’s renal function is normal? Highly doubtful. The drive to get vancomycin troughs between 15-20 is the ID-fellow equivalent for repleting potassium — a constant annoyance, and not always necessary.
• Watch out for ritonavir-related drug-interactions — in particular with inhaled or injectable corticosteroids. Some EHR interaction alerts should not be ignored!
• Still confused about the diagnostic approach to C diff? Here’s a very nice summary of what most micro labs are doing.
• Hemolytic anemia occurring weeks to months after surgery should prompt consideration of transfusion-related babesiosis. Cases may be seen year-round (but most in the summer) and throughout the USA. Median age 65.  Median time to onset of symptoms around 50 days. And no, there is currently no routine screening of blood donors — but as soon as there is a reliable screening test, suspect there will be.
• One important cause of potentially severe hepatitis is herpes simplex virus, which can occur in both immunocompromised and immunocompetent hosts — in the latter, pregnant women seem particularly susceptible. Diagnostic test of choice is blood PCR for HSV DNA.
• The days of Western blot used to confirm HIV diagnosis are numbered, as we head towards this new algorithm. I note that one large commercial lab has already stopped sending the Western blot in favor of the HIV-1/2 differentiation assay — progress!

Rapid fire round: If culture results say “suspected enteric gram negative rods,” it will not be pseudomonas; ditto GNR that grow in both aerobic and anaerobic blood culture bottles (true most of the time) … with disk diffusion susceptibility testing, large numbers indicate greater sensitivity (zone of inhibition), but with MICs, it’s a low number you want … a nice adaptation of the disk diffusion method is the Etest … sending sputum cultures gram stains and cultures on patients with pneumonia after they have been started on antibiotics is all but useless (does not apply to ICU intubated patients) … no one really knows the optimal management of persistent MRSA bacteremia … hepatitis B serologies are an endless source of diagnostic confusion for legions of medical students (and some house staff), so here’s a nifty chart … as we head into summer here in New England, the “doxy deficiency” work-up for febrile adults in the outpatient setting (without an obvious other source) consists of Lyme antibody, anaplasma (not ehrlichia) PCR, and babesia PCR … an organism that is resistant to ceftazidime but sensitive to cefoxitin or cefotetan will be an extended spectrum beta lactamase producer …

Finally, an observation that several commonly used drugs share the fate of trimethoprim-sulfamethoxazole, meaning they may eternally be referred to on rounds by their brand names even though they are all off patent, some for many years. The leaders are:

• Hydromorphone (Dilaudid)
• Levetiracetam (Keppra)
• Furosemide (Lasix)
• Piperacillin-tazobactam (Zosyn)

Ready for 2’45” of fun? Off we go: