HIV and ID Observations

As noted multiple times, many of us ID doctors attend on the general medical service. This offers us a chance to broaden our patient care activities and to work with medical students, interns, and residents.

Boy, that’s fun!

Yes, those of us who attend on medicine enjoy it enormously, though the experience humbles us on a daily basis about what we need to learn in cardiology, nephrology, gastroenterology, rheumatology, hematology, endocrinology — you name it.

Fortunately, the smart trainees (and subspecialty consultants) teach us tons.

Plus, at our hospital we have a co-attending system, meaning my knowledge can be amplified by another experienced doctor — this month an endocrinologist, who has fortunately for all of us never encountered a metabolic disturbance (electrolytes, minerals, glucose) he can’t solve.

https://twitter.com/BrighamChiefs/status/1285652513333686274?s=20

So this week we take a partial break from the COVID-19 coverage, and summarize some ID stuff we’ve chatted about on rounds.

• Meropenem and other carbapenems are not good drugs for treatment of Pseudomonas aeruginosa.. Resistance can develop quickly through alteration of porins or increased efflux pump activity. Ertapenem, for the record, has no reliable activity at baseline. And did you know that ID docs often abbreviate this tricky but common organism as PsA?
• Doxycycline partially protects against the development of C. diff. Yet another a reason why it’s many ID docs’ favorite antibiotic. Bonus podcast at the bottom of this post.
• Diagnostic testing for Lyme disease is a mess. Link is to a very quick slide set. And yes, we still await the final publication of the Lyme IDSA guidelines, released in draft form last year, and expected in the late summer/early fall.
• Diagnosis of another disease caused by spirochetes — syphilis — is also a mess. How many people can clearly explain what a one dilution, one tube, or two-fold change in the RPR means? (Hint, they’re all the same thing.) Link is to another quick slide set. Great new graphic below by the folks from The Clinical Problem Solvers, with a couple of minor suggestions, including a pet peeve — the “need” for LP in ocular/otologic disease. Why do it if you’re going to treat for neurosyphilis regardless of the results?

Very nice graphic! Suggestions:
– Please include the T. pallidum enzyme immunoassay (TP-EIA), which has become the preferred screening test in many places
– Need for LP in ocular/otologic disease is debatable, since we treat for neurosyphilis regardless of results https://t.co/kE2FCihvRm

— Paul Sax (@PaulSaxMD) August 4, 2020

• Ocular syphilis has diverse clinical presentations, most commonly blurred vision, sometimes with photophobia and eye redness. The ophthalmologists will often diagnose uveitis. RPRs are usually high (median titer 1:128 in the linked series), suggesting relatively recent acquisition, but eye involvement can occur at any stage of syphilis.
• Enterobacter and certain other enteric gram negatives may develop resistance to cephalosporins through “de-repression” of a chromosomally mediated beta-lactamase. The confusing thing about this mechanism is that the organisms initially test as susceptible to ceftriaxone, with resistance emerging with noncurative therapy. Cefepime and carbapenems retain activity.
• Sputum is more sensitive than nasopharyngeal samples for diagnosis of COVID-19 in symptomatic patients. Keep this in mind when ruling out the disease in those hospitalized with negative nasopharyngeal swabs; serology may also be useful if symptoms are of 7 days’ duration or longer. Hey, I said this post was a partial break from COVID-19. Can’t be a full break, not yet — boo hoo.
• “Hypervirulent” klebsiella is an increasingly common cause of liver abscess. Unlike other causes of liver abscess, these cases are usually monomicrobial, frequently have metastatic spread, and may have a positive “string test” in the microbiology lab, demonstrating hypermucoviscosity. Disease is more common in Asia.
• Actinomycosis most commonly occurs in cervicofacial, abdominal, pelvic, and thoracic sites. Organism also may be found in relation to IUDs, usually without symptoms. This slowly growing anaerobe takes advantage of anatomic breaks, trauma, or radiation damage, and can cross tissue planes and lead to draining sinus tracts, or masses potentially mistaken for malignancy. Treatment is long-term penicillin (or amoxicillin).
• None of the recommended first-line HIV treatment regimens include the pharmacokinetic boosters cobicistat or ritonavir. Such boosters greatly increase the risk for drug interactions. This means previously popular treatments — in particular the mellifluously named Genvoya — should be retired as initial therapy.
• Aztreonam has a similar mechanism of action as beta-lactam antibiotics (inhibiting cell wall synthesis), but does not cause similar IgE-mediated type-1 hypersensitivity reactions. One possible exception is for patients allergic to ceftazidime, which has a similar side chain (and antibacterial spectrum). Active only against aerobic gram negative infections, aztreonam has few other indications aside from this lack-of-allergy niche. OK, maybe no other indications!
• Chlamydia psittaci is a rare cause of community-acquired pneumonia. And it’s a favorite of ID case conferences and CPCs. Since the primary source is household birds — especially parrots — I was luckily given the following clues in the linked CPC  to frame the discussion, which reads like a ID board exam question:

The patient lived in New England and installed air-conditioning equipment. He owned a ferret and five snakes, to which he fed frozen rabbits and live or frozen rats that he obtained from a pet supply store. His brother owned a healthy puppy. The patient had returned 27 days earlier from a 10-day trip to Hawaii, where he had cut himself on coral while scuba diving. Several of the hotels that he visited had caged parrots in their lobbies.

• The ratio of trimethoprim to sulfamethoxazole in the combination tablets is 1:5. A single strength has 80 mg/400 mg, and a double-strength twice that — hardly anyone knows these arcane facts (except for pediatricians and pharmacists). And aren’t my math skills impressive?  Here’s a tip:  Since no one on rounds wants to say “trimethoprim sulfamethoxazole” (too long), go with “trim-sulfa.” It’s a better abbreviation than the brand names “Bactrim” or “Septra” (both of which should be retired), and it makes more sense than “co-trimoxazole.” Oh, and this is one of several antibiotics with excellent oral absorption.
• Anaerobic bacteria can cause urinary tract infections. Consider these organisms when your standard urine culture is negative, especially in patients with anatomic abnormalities. And trim-sulfa (commonly used for UTIs) won’t be active against these organisms. Check with your microbiology laboratory about how to evaluate further.

All this antibiotic talk! On the first day of rounds this week, during introductions, one of the residents asked us to say our name and our favorite antibiotic.

Good time to replay the antibiotic draft I did with my friend Dr. Rebeca Plank!