Low immunization, antibiotic use fuel strep outbreak

CDC: vaccine strongly recommended for residents

A recent explosive outbreak of multidrug-resistant Streptococcus pneumoniae (MDRSP) that led to three deaths in a McAlester, OK, nursing home emphasizes the need for vaccination of long-term-care residents against an emerging pathogen, reports an investigator with the Centers for Disease Control and Prevention in Atlanta.

During the period of February 6-20, 1996, 12 (16%) of the 74 residents in the nursing home were hospitalized with pneumonia and three subsequently died. The MDRSP outbreak strain -- 23 F -- is included in the pneumococcal vaccine, which is recommended by the CDC for people over age 65. Historically under-utilized due in part to incomplete immunization in all susceptible populations, the pneumococcal vaccine can nonetheless provide a broad measure of protection and reduce invasive infections.1,2 Public health officials did not identify the Oklahoma facility, but reported in the wake of the outbreak that wider use of vaccine is now strongly recommended for institutionalized elderly patients.

"The vaccination coverage was very low in that nursing home," Pekka Nuorti, MD, MPH, CDC Epidemic Intelligence Service officer, tells the Consultant. "There were only four [residents] with documented pneumococcal vaccination in the past five years. This outbreak may have been prevented if the immunization coverage among the residents would have been higher."

In addition to the 12 residents that developed pneumonia, 17 others and two employees were found to be carriers of the resistant strain of MDRSP. Widespread colonization of the residents was thought to be fueled by previous antibiotic use. Antibiotic administration has rapidly expanded in nursing homes, and recently the Society for Health Care Epidemiology of America in Woodbury, NJ, issued some general guidelines for the setting. (See related story p. 88.)

"Certainly the risk of getting pneumonia with MDRSP was clearly associated with past antibiotic use, " Nuorti says. "It was definitely associated with disease, not just with a general overall high level of antibiotics [in the facility]. There was that too -- almost a third of the residents were on antibiotics at one point."

Wide antibiotic use -- particularly of broad-spectrum antimicrobials -- can create "selective pressure" that allows proliferation of a resistant organism once it gains a foothold in an institution.

"The antibiotic use got rid of susceptible bacteria and made room for the drug-resistant one -- that would be my main hypothesis," Nuorti says.

With the emergence of MDRSP strains, outbreaks of pneumococcal disease may become more common, as was the case during pre-antibiotic era, he notes.

"It is interesting to speculate -- are we creating a new nosocomial pathogen with antibiotic use [and] strep pneumo?" he says. "Even though it is a community pathogen, in situations like this it may be that with excessive, inappropriate antibiotic use we may be making strep pneum. a nosocomial-type pathogen."

It is unclear how transmission occurred in the nursing home, since the pathogen can be commonly found in nasopharyngeal cultures of healthy asymptomatic people. However, the identification of colonized health care workers with the outbreak strain raises the possibility of at least some transmission via unwashed hands, possibly during administration of pills during medication rounds, Nuorti says.

"We can only hypothesize they probably would not be washing their hands between putting the pill in the mouth of one resident and going to the next one," he says. "This is something we still need to analyze and look at the distribution of cases in the different areas of the nursing home."

On the other hand, there is also the possibility that residents already colonized with the pathogen developed serious infection after their immune systems were weakened by a gastrointestinal illness that was being reported in the facility. Investigators suspect that preceding gastrointestinal illness may have triggered the outbreak, which ended after residents were given chemoprophylaxis and were immunized.

"Some people complained of having diarrhea and gastrointestinal-type symptoms immediately prior to the onset of their disease," said Mike Crutcher, MD, state epidemiologist in Oklahoma City. "The [MDRSP] was probably spread around the nursing home to some degree, but some people who had it didn't develop disease, and others did. It is not as if every person who came into contact with it developed disease."

Noting that S. pneumoniae is so common a killer of the elderly that it has been termed "the old man's friend," Crutcher said if the resident deaths had occurred over a longer period of time the outbreak may have gone undetected. While reinforcing handwashing and other control measures' the best advice infection control consultants can give client facilities is to screen residents and get them immunized.

"Everybody over the age of 65 should get the vaccine," Crutcher says.

"What we have recommended to nursing homes not only in that area, but statewide is that when people come into your nursing home for the first time you ought to review their [immunization] records."

Cost should not be an issue for individual nursing homes because the vaccine is covered under Medicare, he adds. Such preventive measures are warranted because MDRSP has increased dramatically as a community-acquired infection in recent years, resulting in an ongoing CDC effort to make it a reportable condition in every state and establish a nationwide surveillance system.3

"We haven't really seen strep pneumo outbreaks in nursing homes, especially caused by a strain that is so resistant," Nuorti says. "It may well be that the prevalence of resistance is increasing. We may be seeing more of this, especially with increasing antibiotic use."

References

1. Shapiro ED, Bert AT, Austrian R, et al. The protective efficacy of polyvalent pneumococcal polysaccharide vaccine. N Engl J Med 1991; 325:1453-1460.

2. Centers for Disease Control and Prevention. Pneumococcal polysaccharide vaccine. MMWR 1989; 38:64-68;73-76.

3. Centers for Disease Control and Prevention. Defining the public health impact of drug-resistant Streptococcus pneumoniae: Report of a working group. MMWR 1996 45:(RR-1)1-20. *