Resistant strep strain sparks hospital outbreak

Three deaths due to nosocomial pneumonia

Underscoring that traditional community pathogens can cause nosocomial problems under certain conditions, a deadly outbreak of a multiresistant strain of Streptococcus pneumoniae was recently reported in San Francisco at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC). While the pathogen remains primarily a source of community-acquired infections, the outbreak reminds that it can spread with deadly results among certain patient populations.

"For a long time, we thought that strep pneumo was only a community-acquired infection, but in fact more and more you have outbreaks here and there showing that it could be a nosocomial infection," says Karl Weiss, MD, specialist in infectious diseases and microbiology and head of clinical epidemiology at Hos pital Maisonneuve-Rosemont in Montreal. Weiss and colleagues investigated 16 cases of strep infection that occurred among cardiopulmonary obstructive pulmonary disease patients over an 18-month period that ended in 1996.¹ The pathogen struck in two apparently related but successive outbreaks, infecting nine patients at the initial stage and seven others over a prolonged period, he explains.

"These people were living together in a close environment," he tells Hospital Infection Control. "They were spending time in a big solarium, where they were smoking. So I’m not sure, but that was probably how the bug was transmitted from one patient to the other. I would say it was more prolonged contact between patients rather than the hands of the health care workers."

Fatal cases failed therapy

Most of the patients were diagnosed with acute exacerbation of chronic bronchitis and survived, but three fatal cases occurred in those who developed nosocomial pneumonia. "This population has risk factors, they are not healthy, and because of that they are probably more susceptible to acquiring this type of infection," Weiss says. "The other thing is because these people are being treated with antibiotics for a long time, and they receive antibiotics very often, they are probably prone to be colonized with more resistant strains."

The nosocomial pneumonia deaths included a 78-year-old female and a 66-year-old female, who died of the infections within 24 hours of initiating antibiotic therapy and 48 hours after initiation of therapy, respectively. The other death occurred in a 59-year-old man, who failed to recover after 14 days on ciprofloxacin, was switched to cefuroxime, and died nine days later.

"This case tells you first of all that you can have a nosocomial outbreak with strep pneumo, which is [typically] a community-acquired infection," Weiss says. "Secondly, this can be quite problematic for people with chronic obstructive pulmonary disease, because everybody who had a pneumonia due to this bug died."

The outbreak also was of interest in that it involved microorganisms highly resistant to penicillin and quinolones, he adds. "Basically, over a very short period of time, you had a bug that was resistant to quinolones at a low level but underwent a mutation and became resistant at a higher level," he says. "If you use quinolones with marginal activity against microorganisms — in this case strep pneumo — you are going to favor the emergence of strains that are resistant to this class of antibiotics."

The outbreak was stopped through infection control interventions that included isolating case patients under barrier precautions, he notes. "When you have something like this, first of all try to recognize right away that strep pneumo could be a nosocomial pathogen," Weiss says. "Often, at the beginning, people think of strep pneumo as a community-acquired pathogen. If they have two cases, they think it was acquired in the community, and it is not really related to the hospital. I think if you start having many cases on one ward, you have to think that potentially — and there is some data now — that nosocomial transmission can happen."

Reference

1. Weiss K, Restieri C, Laverdiere M, et al. A nosocomial outbreak of Streptococcus pneumoniae (sp) with reduced susceptibility to fluoroquinolones. Abstract 824. Presented at the 39th Interscience Conference on Antimicrobial Agents and Chemotherapy. San Francisco: Sept. 26-29, 1999.