Resistant strep strains continue troubling rise
November 1, 1999 6 minutes read
Resistant strep strains continue troubling rise
Penicillin on the run; are fluoroquinolones next?
Penicillin-resistant Streptococcus pneumoniae continues to increase in the United States and demonstrates signs of emerging fluoroquinolone-resistant strains in Canada, epidemiologists report.
In the United States, drug-resistant S. pneumoniae — strains of which can be impervious to penicillin and several other first-line antibiotics — climbed from 14% of tested isolates at sentinel hospitals in 1993-1994 to 25% of isolates in 1997, the Centers for Disease Control and Prevention reports.1
"We know that in the late 80s, non-susceptibility to penicillin was zero," says Daniel Feiken, MD, a CDC medical epidemiologist at the Colorado Department of Public Health in Denver. "In 10 years, we have gone from zero to 25%."
The 25% of "non-susceptible" isolates comprised 11.4% of isolates that had intermediate resistance to penicillin and 13.6% that were fully resistant to the drug. "When a pneumococcus is resistant to penicillin, it is often resistant to other antibiotics," Feiken says. "So it may be resistant to erythromycin, cephalosporins, and other anti biotics that are typically used."
Currently, S. pneumoniae is the leading cause of bacterial pneumonia, meningitis, and otitis media in the United States. "About 14% of hospitalized adults will die from their invasive disease," Feiken says. "That will depend on their age and underlying disease status. The older they are and the more underlying disease, the more likely they are to die from their infection." Though traditionally acquired in the community, a recently reported nosocomial outbreak with a resistant strain of S. pneumoniae underscores that the pathogen can pose problems within institutions as well. (See related story, p. 148.) That outbreak strain was highly resistant to penicillin and had reduced susceptibility to some older versions of fluoroquinolone antibiotics.
Another recent study suggests that even later-generation fluoroquinolones may be in jeopardy of losing efficacy if antibiotic pressure continues selecting out resistant strains.2 (See related story, p. 150.) While, in the latter study, the prevalence of fluoroquinolone resistance was low in the isolates tested, the fact that it too was at ground zero only a few years ago is unsettling, Feiken notes. "Fluoroquinolones are used a lot now for pneumonia, and so far pneumococcus has been sensitive," he says. "This could be the beginning of the same thing that happened with penicillin. That is very concerning."
Indeed, what is particularly worrisome about the study is that it shows low levels of resistance began appearing when fluoroquinolone use was less prevalent than it is currently, says one of the authors, Allison McGeer, MD, director of infection control at Mount Sinai and Princess Margaret Hospitals in Toronto.
"These quino lones are being held out as the answer to multiple resistance to other drugs," she says. "These data raise the concern that they are not going to be the answer, and in fact, we may select for resistance much faster for quinolones than we did for penicillin. It really drives home the message that when you are dealing with strep pneumo in the community, any antibiotic that you use is going to get you in trouble. We need to really be [emphasizing] not using antibiotics when we don’t have to, and really being careful about which antibiotics we’re using when we have to."
Indeed, in a familiar refrain, Feiken notes that indiscriminate antibiotic use is likely setting up the kind of selective pressures that have favored the emergence of a variety of other resistant pathogens. "The big problem with pneumococcus is that a lot of people carry it and are colonized with it in the oropharynx, but they are not sick from it," he says. "[Then] people are getting treated with antibiotics for colds and viral bronchitis. There are millions and millions of prescriptions for antibiotics given inappropriately each year. You treat a cold with antibiotics and it knocks out the susceptible [strep pneumo strains], allowing the resistant ones to grow up."
In addition to antibiotic controls, the situation underscores the need for greater use of the pneumococcal vaccine, which is currently recommended for those susceptible age 65 years and older and others at heightened risk, the CDC recommends. The current vaccine contains the six strains of strep pneumo that are most frequently associated with drug resistance. (See Hospital Infection Control, March 1999, pp. 40-41.)
CDC surveillance data indicate that the prevalence of resistant strep pneumo varies widely among geographic regions and even between hospitals in the same region. (See charts, above and p. 151.) The regional differences could reflect both antibiotic prescribing patterns and the circulation of distinct resistant strains, he notes.
"You can’t assume that your hospital, even if it is in the same city, has the same resistance level," he says. "There are certain factors, hospital populations, demographics, or other things that may make even hospitals with the same region have different levels of resistance. When we say that resistance in Tennessee is 38% and in Maryland it’s 15%, that’s a valid statement. But when you look more closely, you can find a hospital in Maryland that has higher resistance than one in Tennessee. It just points out that resistance doesn’t blanket an area uniformly. It will vary depending on the patient population and the hospital you are at."
In general, increasing resistance increases the likelihood of ineffective initial therapy and poorer patient outcomes, he notes. While the jury is still out to some degree on pneumonia, clearly meningitis and otitis media infections caused by resistant strains lead to generally poorer outcomes if the patients are treated with penicillin, he notes. Moreover, the American Academy for Pediatrics recommended in 1997 that clinicians who suspect a child may have pneumococcal meningitis should add vancomycin to cephalosporin regimens, he notes.
In addition to judicious use of antibiotics, the CDC emphasizes that surveillance can increase awareness among clinicians and public health practitioners and assist in targeting areas for intervention. Though the vast majority of infections will come in from the community, CDC surveillance data indicate about 2% of strep pneumonias are likely nosocomial, Feiken says. In addition to controlling spread within hospitals, infection control professionals are increasingly involved with surveillance and education programs targeted at the bug. For example, Linda Booty, RN, BSN, CIC, and other Pittsburgh-area ICPs in the Three Rivers Chapter of the Association for Professionals in Infection Control and Epidemiology undertook a surveillance project.
"It seems to me more of the strep pneumo that I see these days is resistant than it used to be," she says, noting that she and ICP colleagues decided to undertake a surveillance project without identifying their respective hospitals. They conducted a prevalence survey with county health officials and 18 health care facilities over a three-month period in 1998. Of the 487 S. pneumoniae isolates reported in the survey, 32% demonstrated some level of penicillin resistance (21% resistant and 11% intermediate). Overall, patients infected with resistant strains were more likely to be five years or younger (42%) or over 80 (30%). The isolates in the survey came from 23 identified body sites, with sputum and blood being the most common. The majority of the cases were community-acquired, and identified patients were generally put on contact isolation measures to thwart any nosocomial spread, she says.
"It has always been a concern that it would become a nosocomial pathogen. So far, thank heavens, the majority of what we are seeing [is community-acquired]," she says. "But the problem is that as it becomes more resistant, we can’t treat people very efficiently. In the kids, penicillin is the most common thing they use, for ear [infections] especially. Now, we are going to have to be a little more wary of that, knowing the high level of resistance we are seeing in this area."
Indeed, ICPs who participated in the project shared the data with their respective physicians and infection control committees, she says, noting that such region-specific data can be a valuable aid to patient treatment. "For example, at my hospital I brought [the findings] back to my department of pediatrics, family practice, and internal medicine — people that see these types of patients," Booty says. "[ICPs] can have a role in surveillance and in education. And if nothing else, this stresses the need to put more antibiotic controls in our facilities. That’s something ICPs can work very hard toward: appropriate use of antibiotics."
References
1. Centers for Disease Control and Prevention. Geographic variation in penicillin resistance in Streptococcus pneumoniae — selected sites, United States, 1997. MMWR 1999; 48:657.
2. Chen DK, McGeer A, De Azavedo JC, et al. Decreased susceptibility of Streptococcus pneumoniae to fluoroquino lones in Canada. N Engl J Med 1999; 341:233-239.
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