C. difficile disease rates increasing with new strain

November 2005

Rates of Clostridium difficile disease are increasing and so is the severity of those infections.

These changes in C. difficile disease are likely related to the emergence of new epidemic strains. The newest epidemic strain has binary toxin and a delation in a negative regulatory gene (tcdC) as possible virulence factors in addition to toxins A and B. This strain is distinct from the J strain that predominately circulated in U.S. hospitals during the 1980s and 1990s, according to L. Clifford McDonald, MD, a medical epidemiologist in the division of health care quality promotion at the CDC.

“We don’t really know the significance of binary toxin, or the deletion of tcdC. The tcdC deletion could be the cause of this strain’s increased toxin A and B production,” said McDonald at the 43rd Annual Meeting of the Infectious Diseases Society of America, held in San Francisco. “There is also evidence of increased resistance to fluoroquinolones that may be linked to this strain being so successful.”

Increasing rates

C. difficile is transmitted through the fecal-oral route. Health care settings play an important part in the transmission cycle, according to McDonald.

Antibiotic exposure is a major risk factor for disease for both acquisition of the organism and suppression of normal flora, which leads to overgrowth of the organism and expression of toxins, mainly toxin A and toxin B, the two main virulence factors.

Numerous antibiotics have been associated with this risk, including clindamycin, penicillins and cephalosporins.

Because C. difficile is not a nationally reportable disease, the surveillance is not comprehensive, according to McDonald. However, C. difficile is part of the National Nosocomial Infection Surveillance System (NNISS) and data from the ICU section of the NNISS showed rates on a steady rise throughout the 1990s.

A review of acute hospital discharge data from a sample of U.S. hospitals also indicated an increase in C. difficile infections, especially among those aged 64 and older. The increase began around the year 2000, according to McDonald.

The Northeast has always had higher rates of C. difficile disease, but there have been dramatic increases in the Midwest and South as well, according to McDonald.

Increasing severity

Over the past few years, a change has occurred regarding the severity of C. difficile infections. One of the earliest reports came from Pittsburgh and described how severe disease rates rose from 1.6% to 3.2%, with 26 colectomies and 18 deaths reported in 2000-2001 alone.

Then, health officials in Quebec reported C. difficile cases there. A report suggests that as many as 3,000 C. difficile–related deaths occurred in 2003-2004, according to McDonald.

A survey revealed that practicing infectious disease physicians in the United States perceive that C. difficile cases are becoming more frequent and more severe in this country as well.

“This trend was observed across the United States and was not limited to one particular geographic region,” McDonald said.

There were 531 survey respondents and 201 (38%) of the respondents indicated that they experienced an increased case load over the previous six months and they estimated a total of just over 3,000 cases seen during that six-month span. Another 210 (40%) survey respondents perceived an increased severity in the types of cases.

Although McDonald mentioned that the data may have been biased because it was based on memory and perceptions, it does suggest that increased severity of C. difficile disease is being seen in this country.

The rates and apparent severity increases may be due to the emergence of an epidemic strain of C. difficile with special virulence or antimicrobial resistance properties, according to McDonald.

“The role of resistance may not be quite as obvious, but it’s been shown previously that certain epidemic strains have acquired resistance to other antibiotics – not antibiotics used to treat C. difficile – but for example clindamycin,” he said. “C. difficile did not start out being resistant to clindamycin. It was an acquired form of resistance, and when strains acquired this resistance they became more fit for causing outbreaks in hospitals where this antibiotic was used.”

Studying outbreaks

Based on this hypothesis, McDonald’s team investigated whether there is an emerging strain with increased resistance or virulence. They began characterizing C. difficile isolates from hospitals with recent outbreaks. The isolates were typed; the team searched for molecular markers for increased virulence and conducted antibiotic susceptibility testing.

The outbreaks occurred between 2001 and 2004 in eight hospitals from six states, where researchers detected outbreaks by noting increases in the number of positive results in routine laboratory tests for C. difficile.

“In the United States that test is shifting from an A-only immunosorbent assay to an A-B assay,” he said.

Researchers in the laboratory of Dale N. Gerding, MD, professor of medicine at Loyola University Chicago Stritch School of Medicine, conducted the strain typing on the isolates by restriction enzyme analysis. Pulsed field gel electrophoresis (PFGE) was also performed, along with toxin typing, which involves cutting up the DNA to look for polymorphisms in the pathogenicity locus, or PaLoc. In addition to toxin A and toxin B, polymerase chain reaction (PCR) was used to find binary toxin.

“The binary toxin is a possible additional virulence factor for C. difficile,” he said, adding that it is similar to a toxin found in Clostridium perfringens.”

The gene for binary toxin is located outside the PaLoc, where toxins A and B are located. McDonald said his team also looked for variations in the gene known as tcdC.

“This gene is a downstream negative regulator in the PaLoc next to toxin A and B genes; it is thought to suppress toxin production. PCR was used to look for recently described deletions in tcdC that could lead to increased toxin production,” he explained.

McDonald said researchers also performed susceptibility testing using E tests, focusing mainly on fluoroquinolones because of recent outbreaks associated with those drugs.

The research revealed a common epidemic strain, a similar strain from dispersed geographic regions, by PFGE across these hospitals in the study. There have been outbreaks of this strain from Maine to Georgia and Oregon.

In addition, the same strain was found in a historic database of over 6,000 isolates. There were 14 patient-isolates of this same strain in the database and these dated back to 1984.

“A previously uncommon strain that has been around as a minor player since the 1980s now has become an epidemic strain,” McDonald said.

The epidemic strain accounted for at least 50% of the isolates tested from five of the eight outbreak hospitals, and a sizable proportion of isolates from other hospitals, suggesting that in most hospitals the increase in cases observed during the outbreaks could be explained by the prevalence of the epidemic strain, according to McDonald.

The epidemic strain was toxinotype III. The most common, or “wild type,” toxinotype is toxinotype 0; 80% of isolates in the past have been toxinotype 0. There are currently over 20 different toxinotype variants that have been identified.

“In the past, toxinotype III has been an infrequent finding. This epidemic strain is also binary toxin positive and it has a 18-base pair deletion and tcdC; and none of these characteristics were common in the other strains,” he said.

Compared with current nonepidemic strain isolates and historic isolates of the epidemic strain, current isolates of the epidemic strain are more resistant to fluoroquinolones.

“This is a new development,” McDonald said.

The CDC recommends that hospitals conduct surveillance for C. difficile-associated disease and consider measures to track outcomes. Early diagnosis and treatment appear to be important in reducing severe outcomes and not every hospital has noticed severe outcomes, according to McDonald. In those hospitals where severe outcomes have been noted, the frequency of such outcomes seem to decline with the initiation of early diagnosis and treatment of cases.

Recommendations

Strict infection control is necessary, including contact precautions for known C. difficile patients, and an environmental cleaning and disinfection strategy that includes the use of dilute bleach to inactivate C. difficile spores. Because alcohol is ineffective in killing C. difficile spores, it is prudent for health care workers to wash their hands with soap and water rather than clean them with an alcohol-based waterless hand sanitizer when caring for patients with C. difficile–associated disease during an outbreak. “In addition, further research is needed in the area of restricting antimicrobials, in this case fluroquinolones, to control outbreaks of C. difficile associated disease caused by the epidemic strain. It has been shown that several outbreaks have been associated with the use of fluoroquinolones” he said.

Norovirus

Norovirus is the most common cause of acute gastroenteritis. This illness has a short incubation period, multiple routes of transmission and is stable in the environment. Diagnostic tests are not readily available. There is a reverse-transcriptase PCR that the CDC is trying to get more state laboratories to use, at least in determining the etiology of outbreaks, according to McDonald.

There is also an enzyme-linked immunosorbent assay (EIA) that might be useful for confirming the etiology of an outbreak.

One handles outbreaks of norovirus differently than C. difficile. The control of norovirus outbreaks in hospitals has more to do with relocating patients, closing wards or placing affected health care workers.

Just like with C. difficile, norovirus is most common among those 64 years and older.

There is a difference in epidemiology of noroviruses in the United States and Europe. Cases are more likely to occur in acute care facilities outside the United States. There is a predominant international strain recognized on both sides of the Atlantic but has it not taken off in this country.

Acute care hospital design and patient placement may be one reason why U.S. rates of norovirus infection are lower. Acute care hospitals in some European nations tend to have larger rooms with more patients sharing the same bathroom, according to McDonald.

Control measures are especially important with norovirus because it can quickly spread through hospital staff, which makes it different from C. difficile. Single patient rooms and private bathrooms probably help decrease the spread of norovirus. There have been some reports of aerosolization of the virus, but the data are unsupported. However, the CDC does recommend wearing a surgical mask when cleaning up feces or vomit from a patient with norovirus infection.

For more information:

• McDonald C and Valenti AJ. Outbreaks in health care: focus on C. difficile and Norovirus. Session 74. Meet the Professor. Presented at the 43rd Annual Meeting of the Infectious Diseases Society of America. Oct. 6-9, 2005. San Francisco.
• McDonald LC. Clostridium difficile: responding to a new threat from an old enemy. Infect Control Hosp Epidemiol. 2005;26:672-675.
• Pepin J, Saheb N, Coulombe MA, et al. Emergence of fluoroquinolones as the predominant risk factor for Clostridium difficile-associated diarrhea: a cohort study during an epidemic in Quebec. Clin Infect Dis. 2005;41:1254-1260.
• Pepin J, Valiquette L, Cossette B. Mortality attributable to nosocomial Clostridium difficile-associated disease during an epidemic caused by a hypervirulent strain in Quebec. CMAJ. 2005;173:1037-1042.
• Warny M, Pepin J, Fang A, et al. Toxin production by an emerging strain of Clostridium difficile associated with outbreaks of severe disease in North America and Europe. Lancet. 2005 Sep 24-30;366(9491):1079-84.
• Dallal RM, Harbrecht BG, Boujoukas AJ, et al. Fulminant Clostridium difficile: an underappreciated and increasing cause of death and complications. Ann Surg. 2002; 235 : 363-370.
• Klaassen CH, van Haren HA, Horrevorts AM, et al. Molecular fingerprinting of Clostridium difficile isolates: pulsed-field gel electrophoresis versus amplified fragment length polymorphism. J Clin Microbiol. 2002; 40:101-104.
• Spigaglia P, Mastrantonio P. Molecular analysis of the pathogenicity locus and polymorphism in the putative negative regulator of toxin production (TcdC) among Clostridium difficile clinical isolates. J Clin Microbiol. 2002;40:3470-3475.
• Stubbs S, Rupnik M, Gibert M, et al. Production of actin-specific ADP-ribosyltransferase (binary toxin) by strains of Clostridium difficile. FEMS Microbiol Lett. 2000;15:307-312.
• Johnson S, Samore MH, Farrow KA, et al. Epidemics of diarrhea caused by a clindamycin-resistant strain of Clostridium difficile in four hospitals. N Engl J Med. 1999;341:1645-1651.
• Rupnik M, Avesani V, Janc M, et al. A novel toxinotyping scheme and correlation of toxinotypes with serogroups of Clostridium difficile isolates. J Clin Microbiol. 1998;36:2240-2247.
• Clabots CR, Johnson S, Bettin KM, et al. Development of a rapid and efficient restriction endonuclease analysis typing system for Clostridium difficile and correlation with other typing systems. J Clin Microbiol.1993; 31:1870-1875.