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Up-and-Coming Bugs: Evaluating the Latest Infectious Trends
By Kris Ellis
As all infection control practitioners(ICPs) know, the world of dangerous microorganisms is in a state of constantevolution and flux. New threats must be closely monitored along with those thatare well established, and maintaining an up-to-date base of knowledge can be thedifference between success and failure in terms of outbreak prevention andtreatment. Currently, several pathogens are gaining notoriety for the potentialhavoc they can wreak in hospitals and communities alike.
Community-acquired methicillin-resistant Staphylococcusaureus (CA-MRSA) is a relatively recent phenomenonthat has firmly entrenched itself in many locations. The first thing to noteis variable penetration into different areas, says Trish Perl, MD, MSc,associate professor of medicine at Johns Hopkins University and hospitalepidemiologist at Johns Hopkins Hospital. Perl is also president-elect of theSociety of Healthcare Epidemiology of America (SHEA). She points out that somecommunities such as Baltimore, Dallas, and Chicago see CA-MRSA frequently, whileit is relatively rare in others. Perl notes that the pathogen initiallypresented primarily in children as skin and soft tissue infections and alsotoxic shock-like presentation. With adults, again weve seen similarpresentations with a lot of skin and soft tissue stuff. Also, some veryimpressive necrotizing pneumonias and pneumonic processes, some of which wereclearly post-influenza. People could have septic shock, multi-organ failure, endup on ventilators for long periods of time these are very differentpresentations than we have seen with hospital-acquired MRSA. This is not at allto say that hospital-acquired MRSA is not a bad infection it is, but we justreally didnt see these very impressive acute presentations, and thepredominance of skin and soft tissue.
Perl cites anecdotal reports of CA-MRSA transmission amongfamilies as an interesting phenomenon as well. She also says there is much to belearned about how the bug is spread and how it can be controlled. The nasalcarriage data suggests that the epidemiology of this may be different, and itsnot clear what the ecologic niche is right now. Perl notes that even withouta significant amount of data showing that people are nasal carriers,decolonization using Mupirocin is often performed. I think were missing two wonderful opportunities oneis to understand the epidemiology better and two, to use this as an educationaltool; you really have to culture before you treat. From an epidemiologic pointof view, I think thats very important.
The other thing thats interesting about this organism isthat we dont understand the role of the environment, but we know itsimportant, Perl continues. She points to a study from the NewEngland Journal of Medicine describing an MRSAoutbreak among members of the St. Louis Rams football team as illustration.1Perl says pushing for improved hygiene will be important in combating CAMRSA, aswill taking the focus off of treatment with Mupirocin.
Nancy Church, RN, BSN, MT (ASCP), CIC, director of infectioncontrol at Portland, Ore.- based Providence St. Vincent Medical Center, saysCA-MRSA in her community seems to be related to environmental factors as well.We started seeing it here in our ER with what were known as spider bitesprobably about three years ago, she says The ER doesnt culture everyboil they would lance, but they did culture a few of them and suddenly westarted to see MRSAs in this population. So when we looked at the first 10patients that we saw, I and another colleague found that we were seeing theseprimarily in meth amphetamine users. A common characteristic of this type ofpopulation involves a large number of people sharing a relatively small livingspace. I notified the county health department that this is what we wereseeing and then they took a look at their clientele in which they were startingto see the same thing, and they also found that it was linked to behavioralhealth issues with drug use. Those were our first cases that we saw and fromthere its certainly gone on to spread out into a much larger segment of thepopulation.
Church used the information she discovered to encourage the ERto perform cultures in order to determine what antibiotics the strains would besensitive to. The historical treatment that was used was to lance the boiland put them on Keflex, and I think lancing the soft tissueabscess was the key and that the Keflex wasnt really doing much of anything,she explains. So with some education and with the infectious diseasephysicians working with them here, we managed to primarily switch them todifferent antibiotics depending on the sensitivity, with Bactrim being one ofthe main treatments.
The other thing thats really important about thesestrains is that theyre different theyre susceptible to moreantibiotics, Perl explains. Theyve got this SCC type IV cassette whichis smaller; it cant hold as many resistance genes, but these strains carry alot more toxins than other strains. Everyone was talking about something calledthe Panton-Valentine Leukocidin (PVL), but when you look at the data, theycarry a lot of different potential toxins. Thats important. Thats whatsprobably leading to these dramatic presentations of clinical disease that I wastalking about. We have to look at new prevention and control strategies.
Sheldon Kaplan, MD, professor and vice chairman for clinicalaffairs in the Department of Pediatrics at Baylor College of Medicine, as wellas chief of the infectious disease service at Texas Childrens Hospital, notesthat CA-MRSA has been an issue in the Houston area for years. Weve beenstudying this very extensively for the past five years and we have, at TexasChildrens Hospital (TCH), each year about 1,700 to 1,800 kids who are seenfrom the community with a staph infection, and 75 percent of those aremethicillin resistant, so 75 percent of the staphs in our community in kids aremethicillin resistant, he says. Thats just at TCH, so then youve gotall the private offices, clinics, and pediatricians who are seeing kids withskin and soft tissue infections that are mild enough that they dont needsurgery for drainage of an abscess theyre being taken care of by theirown physicians or clinics.
So we know that the infections that we see are just the tip ofthe iceberg. The vast majority 95 percent of the MRSAs from the community are associated with skin and soft tissue infections. Many of those kids, asI mentioned, end up in the hospital and need to have an incision and drainageand then theyre here for a few days on IV therapy. Five percent of those kidshave serious invasive infections, such as bone, muscle, and lung infections, andI think weve had six deaths as well, so its a very serious problem.
Kaplan notes that many clinicians are struggling with how tohandle this emerging issue. Some people are promoting surveillance cultureson all patients who come in the hospital to see if theyre colonized and thenput them into isolation; I dont think we really know what the right answeris, he says. The community strains are now circulating in many areas ofthe country in hospitals. Nosocomial staph infections, many of these are now the strainsthat are from the community MRSA isolates from the community are now beingassociated with hospitalacquired infections and Im sure this is going toincrease with time.
Extended-spectrum beta-lactamases (ESBL)
Extended-spectrum beta-lactamases (ESBLs) are described as arapidly-evolving group of beta-lactamases that are able to hydrolyzethird-generation cephalosporins and aztreonam, but are inhibited by clavulanic acid.2ESBLs provide a sobering illustration of the ability ofgram-negative bacteria to develop new patterns of antibiotic resistance. Thereare currently a very limited number of options for antibiotic treatment ofESBL-producing organisms.
ESBLs arent getting as much attention, at least in thelay press, but theyre potentially as scary if not scarier organisms [thanCAMRSA], Perl says. This actually can involve a group ofgram-negatives, so its not just one bug, but its multiple bugs Coxiella, E. coli, there are many different organisms that can produce these.
Proper identification of ESBLs and understanding theirsignificance in certain serious infections is vital in order to avoid treatmentfailures, according to Perl. The Clinical and Laboratory Standards Institute(CLSI) has developed guidelines for the detection of ESBLs produced by E. coli, Klebsiellapneumoniae, Klebsiellaoxytoca, and Proteus mirabilis. These guidelinesrecommend the use of K. pneumoniae ATCC 700603 (an ESBL producer) as a qualitycontrol organism in tests to detect the presence of ESBLs.3
What ICPs might be seeing are people who arentresponding appropriately to therapy for gram-negative infections, Perl says.That requires education to make sure that people who are prescribers actuallyunderstand what an ESBL is. The other thing to say, and my perspective on MRSAand ESBLs is identical, is that again, this is an organism thats easilytransmitted; it can be transmitted on hands just like MRSA and we should beidentifying these people and isolating it. Im a firm believer that isolationin the healthcare setting for ESBLs is important, especially in high-risksettings like ICUs where its really easy for this to be transmitted frompatient to patient.
Church notes that ESBLs were quite rare in her facility untilabout a year ago, when they began to increase in number. In our case they areprimarily seen in urine cultures, and these are often in patients who have beenexposed to multiple antibiotics because theyve got underlying conditions,she says. Many physicians didnt really understand what this was, so wehave an electronic system here that we put in the computer where, once weveidentified something, it will pop up again if theyre readmitted. The purpose of that is not so much just to designate thepatient with an isolatable type of issue, but more to inform the physicians sothey can know when they have to pay attention to the antibiotics they mayneed to talk to pharmacy or ID. Thats how we utilize it here.
Other Resistant Organisms
To me acinetobacter is one of the scariest ones thatsout there, Perl says. Its a pathogen that really came into its ownabout three or four years ago in New York City where there was an outbreak thatinvolved 10 or 12 hospitals that shut down units to actually get control of it.I think whats been most concerning is that this organism has become resistantto everything except a drug called polymyxin B. That drug was developed in the40s and I had never used it until last year. Its got a lot of associatedtoxicities with it. This is a pathogen that weve had in Baltimore since about1995, and there are a lot of places that are seeing this.
Acinetobacter baumannii is agram-negative bacillus that commonly colonizes aquatic environments. The organism is often cultured from hospitalized patientssputum or respiratory secretions, wounds, and urine. Acinetobacter can also befound in irrigating solutions and intravenous solutions. Infections oftenmanifest as nosocomial pneumonia, infections associated with continuousambulatory peritoneal dialysis, or catheter-associated bacteruria. Acinetobacter pneumonias often occur as outbreaks and areusually associated with colonized respiratory support equipment or fluids.4
It has an unbelievable ability to contaminate theenvironment much more so than MRSA, Perl continues. You have to throwout tons of equipment because you cant figure out where it is. Weveactually been criticized here because we have a pretty draconian approach tothat organism we require oneon- one nursing and people signing in and out ofrooms, but weve had no transmission since weve done that. The thing thatsalso concerning to me is that now as were getting more and more data, atleast at our institution, that one of the sources of this is patients who comein from nursing homes and chronic ventilation facilities.
Hospital-acquired MRSA is, of course, still a significantconcern as well. Church explains that, at her facility, studying MRSA in greaterdetail has proven to be beneficial. We had some work done here that showedour fluoroquinolone use was directly contributing to our increase in some MRSAwe were seeing, so we revised some antibiotic prescribing habits in the ER totry and reduce that, she says. We did a study in 2002-2003 to try andunderstand where ours was coming in from. We looked at all the patients who wereadmitted to the clinical care unit for five months with active surveillancecultures and learned that the primary source of that was coming from residentialfacilities such as nursing homes, foster homes, and those types of institutionswhere you have large numbers of people living together.
As a result of these findings, Church says efforts were madeto work with and educate staff at these types of facilities in order to promotehand hygiene. We still have some problems, but I think there have been somesignificant successes. In Oregon we have short lengths of stay, and that wasoffset by using our nursing homes and our rehabilitation centers, so when webegan to see patients who were having surgery and coming back in with MRSA, andwe didnt believe it had been acquired in the facility, we brought a lot ofnursing homes together to take a look at what was going on and tell them what wewere seeing from our side and determine what we could do to help them. Thatprecipitated a number of changes that weve made, which I think have helped,but the education on the alcohol hand gels in particular, and goodcommunication, were most important.
Ultimately, contending with antimicrobial-resistant organismswill continue to be a significant challenge for clinicians. The bugs aresmarter than we are; theyll adapt and produce toxins and become resistant they will keep on adapting and were dealing with a more compromisedpopulation so well have new and evolving challenges, Perl says. I thinkthe thing thats universal across all of these is that theres a veryimportant role for very basic infection control and prevention strategies. Ipersonally think that does involve surveillance.
Theres a very emotional debate thats going on right nowin the infection control community about whether or not to do surveillance, andthe whole concept of this is just the tip of the iceberg. Being extremelyproactive and admitting that those bugs are there has really helped preventtransmission in our institution. The other thing to point out about it is thattraditionally people thought it was the academic centers where all theresistance and bad bugs were created, but thats no longer true itsvery clear that theyre coming in from long-term care facilities, from thecommunity, day care centers, and other places.
In addition to antibiotic resistance, communicable diseasesare an ongoing concern for ICPs. From the apparent reemergence of certaindiseases to decreases in vaccination rates in subsets of the population, thepotential for an outbreak is always a concern for clinicians.
Pertussis (whooping cough) is one such condition that hasreceived a seemingly increased amount of attention as of late. Wererecognizing it more, probably because of better diagnostic techniques, Kaplansays. There may be some issues with regard to seeing it more because ofwaning immunity, especially in adolescents and older individuals, because nowtheres some pretty good evidence to show that its college-age people whoare a reservoir for this organism. There are three or four studies now that showthat if you have a college-age individual or an adult whos coughing for twoor three weeks and its unexplained, pertussis is probably responsible for 25percent of these cases.
Kaplan notes that it is difficult to make that diagnosis inolder individuals. Diagnosis in children, however, has improved recently. Inthe past, you mainly had culture or fluorescent antibody testing, neither ofwhich was very sensitive, but now you have polymerase chain reaction (PCR),which seems to be very good and is probably the lab test of choice in provingthat youve got a pertussis infection, he says. So its probably acombination of better diagnostics as well as some waning immunity, thus therecommendation for immunizing adolescents and adults with this new acellularpertussis vaccine.
Churchs community has seen pertussis outbreaks, and shesays many adults thought they were protected from childhood vaccination. Learning that the vaccine wanes in its effectiveness overtime was kind of a surprise to people. We also have areas where weve haddifficulty in getting immunizations into certain sub-pockets of the population,and so we would see an occasional pertussis case pop up there and then spread.Weve done a huge amount of work to educate people and I think the advent ofthe newer vaccine that can be given to adolescents and young adults will beextremely helpful.
In October 2005, three children in Minnesota were found to beinfected with the polio virus. All members of the same family, which is part of the Amishcommunity, the children had not been vaccinated against the disease. MinnesotaDepartment of Health officials said the virus strain appears to be a variant ofthe one used in oral (live) polio vaccine. Before this version of the vaccinewas discontinued in 2000, it caused approximately eight cases of paralytic polioper year in the United States. The current version is injected using a killedpolio virus.
Dealing with outbreaks in populations that dont believe invaccination can be extremely challenging for the healthcare community. Ifsomething starts in those populations then you have a whole group of people whoare susceptible and that can be really problematic, Church says. Also,with the mobility of society today, it can complicate the situation.
1. Kazakova, SV, et al. A clone of methicillinresistantStaphylococcus aureus among professional football players. NEngl J Med. 2005 Feb 3;352(5):468-75.
2. Paterson DL, Bonomo RA. Extended-spectrum beta-lactamases:a clinical update.
Clin Microbiol Rev. 2005Oct;18(4):657-86, table of contents.
3. Clinical and Laboratory Standards Institute. 2005. Performance standards for antimicrobial susceptibilitytesting. Fifteenth international supplement M100-S15. Clinical and LaboratoryStandards Institute, Wayne, Pa.
Some clinicians may have dismissedtuberculosis (TB) as qualifying as an emerging disease these days, but until itis completely eradicated, it remains a concern for public health officials.
Consider these facts from the World Health Organization (WHO):
TB is a contagious disease, and likethe common cold, its transmission is airborne. When infectious people cough,sneeze, talk, or spit, they propel TB bacilli into the air; a person needs onlyto inhale a small number of these bacteria to be infected. Left untreated, eachperson with active TB disease will infect on average between 10 and 15 peopleevery year. But people infected with TB bacilli will not necessarily become sickwith the disease. The immune system walls off the TB bacilli which,protected by a thick waxy coat, can lie dormant for years. When an individualsimmune system is weakened, the chances of becoming sick are greater.
Starting in the 1940s, scientists discovered the first ofseveral medicines now used to treat TB. As a result, TB slowly began to decreasein the United States. But in the 1970s and early 1980s, the country let down itsguard and TB control efforts were neglected. As a result, between 1985 and 1992,the number of TB cases increased. However, with increased funding and attentionto the TB problem, there has been a steady decline in the number of persons withTB since 1992. But TB is still a problem; more than 14,000 cases were reported in 2003 in the UnitedStates.
Until 50 years ago, there were no medicines to cure TB. Now,strains that are resistant to a single drug have been documented in everycountry surveyed; strains of TB resistant to all major anti- TB drugs also haveemerged. A particularly dangerous form of drug-resistant TB ismulti-drug-resistant TB (MDR-TB), which is defined as the disease caused by TBbacilli resistant to at least isoniazid and rifampicin, the two most powerfulanti-TB drugs. Rates of MDR-TB are high in some countries, and threaten TBcontrol efforts.
The most important way to keep from spreading TB in a hospitalsetting is taking isolation measures with patients who are suspected or known TBcarriers. Patients placed in isolation should remain in their isolation roomswith the door closed. To prevent the escape of droplet nuclei, the TB isolationroom should be maintained under negative pressure. If possible, diagnostic andtreatment procedures should be performed in the isolation rooms to avoidtransporting patients through other areas of the facility. If patients who mayhave infectious TB must be transported outside their isolation rooms formedically essential procedures that cannot be performed in the isolation rooms,they should wear surgical masks that cover their mouths and noses duringtransport. Persons transporting the patients do not need to wear respiratoryprotection outside the TB isolation rooms. The number of persons entering anisolation room should be minimal. All persons who enter an isolation room shouldwear respiratory protection; the patients visitors should be givenrespirators to wear while in the isolation room, and they should be givengeneral instructions on how to use their respirators. Personal respiratoryprotection should be used by persons entering rooms in which patients with knownor suspected infectious TB are being isolated, persons present duringcough-inducing or aerosol-generating procedures performed on such patients, andpersons in other settings where administrative and engineering controls are notlikely to protect them from inhaling infectious airborne droplet nuclei.Respiratory protective devices used in healthcare settings for protectionagainst M. tuberculosis should meet the following standard performance criteria:the ability to filter particles 1mm in size in the unloaded state with a filterefficiency of greater or equal to 95 percent, given flow rates of up to 50L perminute; the ability to be qualitatively or quantitatively fit tested in areliable way to obtain a face-seal leakage of less than or equal to 10 percent;the ability to fit the different facial sizes and characteristics of HCWs; and the ability to be checked for face-piece fit, in accordancewith standards established by the Occupational Safety and Health Administration(OSHA) and good industrial hygiene practice, by HCWs each time they don their respirators.