Antimicrobial Usage & Spread of Resistance

Glen Tamura gtamura at u.washington.edu
Wed Jan 22 19:29:38 EST 1997


Since I happening to prepare for a talk on antimicrobial resistance, I
thought I'd throw my two cents in. 

Q: Are community acquired infections by resistant bacteria rare?  
A: Not any more, with the rise of resistant pneumococci. Recent data
suggest that 24% of pneumococci isolated from outpatients in the United
States were not susceptible to penicillin (14.1% intermediate, 9.5%
high-level resistance, Doern GV et al, Antimicrob Agents Chemother
40:1208-13, 1996).

Q: Where did these bacteria arise from? 
A: Steven Projan is correct, that most of these isolates appear to first
appear in third world countries. Any theories on why this might be so are
purely speculative and without any experimental evidence to back them up. 
 
Q: What percentage of kids get antibiotics for viral infections? 
A: A recent study (Arnold KE et al, J Pediatr 128:757-764, 1996) found
that nearly 50% of children who were see in pediatricians offices for
upper respiratory infections and did NOT have otitis media still got
antibiotics. Admittedly, a fair proportion of these may have had sinusitis
or bronchitis, for which antibiotic therapy would be appropriate. On the
other hand, I very  much doubt that anywhere near half of them did. 

Q: Does use of antibiotics in the outpatient setting select for resistant
bacteria?
A: Recent data are quite convincing that antibiotic usage increases the
rate of carriage of resistant pneumococci by approximatey two-fold (Arnold
et al, see ref above, and B'edos JP et al, Clin Infect Dis 22:63-72,
1996). Furthermore, the risk of carriage of resistant pneumococci in a
highly treated population (patients with sickle cell anemia take
prophylactic penicillin on a daily basis) is 62%! Pretty impressive. 

Q: Steven Projan raises the argument that viral diseases are often
secondarily infected with bacteria, and that "if only 20% of such
infections are really bacterial - do we let those 20% suffering from
bacterial infections get sicker until we get the culture results? Is that
smart practice? Since when does the Hipocratic (sic) oath say "Do no
good"? 
A: It depends on the natural history of the bacterial infection you are
talking about. 
	For serious infections, such as meningitis or pneumonia, empiric
antibiotic therapy for suspected cases is absolutely necessary, even if
the risk of disease (pending culture results) is only 5%, let alone 20%. 
	However, the vast majority of antibiotic prescriptions in the
pediatric age group are for otitis media, sinusitis, and bronchitis.
The natural history of these diseases is relatively benign, and delaying
therapy for a few days or even a week will not result in any long-term
harm to the patient. 
	The average child will have approximately 10-15 upper respiratory
viral infections in each of their first two years. It seems silly to
prescribe antibiotics for all of these is imprudent. This will double the
risk for THAT PATIENT's developing resistant pneumococcal carriage, thus
making it much harder to treat the patient when they really need therapy. 

Glen S. Tamura, M.D., Ph.D.
Division of Infectious Disease
Department of Pediatrics
University of Washington
Seattle, WA  98105




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