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 constant evolution and flux. New threats must be closely monitored along with those that are well established, and maintaining an up-to-date base of knowledge can be the difference between success and failure in terms of outbreak prevention and treatment. Currently, several pathogens are gaining notoriety for the potential havoc they can wreak in hospitals and communities alike.
Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a relatively recent phenomenon that has firmly entrenched itself in many locations. The first thing to note is variable penetration into different areas, says Trish Perl, MD, MSc, associate professor of medicine at Johns Hopkins University and hospital epidemiologist at Johns Hopkins Hospital. Perl is also president-elect of the Society of Healthcare Epidemiology of America (SHEA). She points out that some communities such as Baltimore, Dallas, and Chicago see CA-MRSA frequently, while it is relatively rare in others. Perl notes that the pathogen initially presented primarily in children as skin and soft tissue infections and also toxic shock-like presentation. With adults, again weve seen similar presentations with a lot of skin and soft tissue stuff. Also, some very impressive necrotizing pneumonias and pneumonic processes, some of which were clearly post-influenza. People could have septic shock, multi-organ failure, end up on ventilators for long periods of time these are very different presentations than we have seen with hospital-acquired MRSA. This is not at all to say that hospital-acquired MRSA is not a bad infection it is, but we just really didnt see these very impressive acute presentations, and the predominance of skin and soft tissue.
Perl cites anecdotal reports of CA-MRSA transmission among families as an interesting phenomenon as well. She also says there is much to be learned about how the bug is spread and how it can be controlled. The nasal carriage data suggests that the epidemiology of this may be different, and its not clear what the ecologic niche is right now. Perl notes that even without a significant amount of data showing that people are nasal carriers, decolonization using Mupirocin is often performed. I think were missing two wonderful opportunities one is to understand the epidemiology better and two, to use this as an educational tool; you really have to culture before you treat. From an epidemiologic point of view, I think thats very important.
The other thing thats interesting about this organism is that we dont understand the role of the environment, but we know its important, Perl continues. She points to a study from the New England Journal of Medicine describing an MRSA outbreak among members of the St. Louis Rams football team as illustration.1 Perl says pushing for improved hygiene will be important in combating CAMRSA, as will taking the focus off of treatment with Mupirocin.
Nancy Church, RN, BSN, MT (ASCP), CIC, director of infection control at Portland, Ore.- based Providence St. Vincent Medical Center, says CA-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 bites probably about three years ago, she says The ER doesnt culture every boil they would lance, but they did culture a few of them and suddenly we started to see MRSAs in this population. So when we looked at the first 10 patients that we saw, I and another colleague found that we were seeing these primarily in meth amphetamine users. A common characteristic of this type of population involves a large number of people sharing a relatively small living space. I notified the county health department that this is what we were seeing and then they took a look at their clientele in which they were starting to see the same thing, and they also found that it was linked to behavioral health issues with drug use. Those were our first cases that we saw and from there its certainly gone on to spread out into a much larger segment of the population.
Church used the information she discovered to encourage the ER to perform cultures in order to determine what antibiotics the strains would be sensitive to. The historical treatment that was used was to lance the boil and put them on Keflex, and I think lancing the soft tissue abscess was the key and that the Keflex wasnt really doing much of anything, she explains. So with some education and with the infectious disease physicians working with them here, we managed to primarily switch them to different antibiotics depending on the sensitivity, with Bactrim being one of the main treatments.
The other thing thats really important about these strains is that theyre different theyre susceptible to more antibiotics, Perl explains. Theyve got this SCC type IV cassette which is smaller; it cant hold as many resistance genes, but these strains carry a lot more toxins than other strains. Everyone was talking about something called the Panton-Valentine Leukocidin (PVL), but when you look at the data, they carry a lot of different potential toxins. Thats important. Thats whats probably leading to these dramatic presentations of clinical disease that I was talking about. We have to look at new prevention and control strategies.
Sheldon Kaplan, MD, professor and vice chairman for clinical affairs in the Department of Pediatrics at Baylor College of Medicine, as well as chief of the infectious disease service at Texas Childrens Hospital, notes that CA-MRSA has been an issue in the Houston area for years. Weve been studying this very extensively for the past five years and we have, at Texas Childrens Hospital (TCH), each year about 1,700 to 1,800 kids who are seen from the community with a staph infection, and 75 percent of those are methicillin resistant, so 75 percent of the staphs in our community in kids are methicillin resistant, he says. Thats just at TCH, so then youve got all the private offices, clinics, and pediatricians who are seeing kids with skin and soft tissue infections that are mild enough that they dont need surgery for drainage of an abscess theyre being taken care of by their own physicians or clinics.
So we know that the infections that we see are just the tip of the iceberg. The vast majority 95 percent of the MRSAs from the community are associated with skin and soft tissue infections. Many of those kids, as I mentioned, end up in the hospital and need to have an incision and drainage and then theyre here for a few days on IV therapy. Five percent of those kids have serious invasive infections, such as bone, muscle, and lung infections, and I think weve had six deaths as well, so its a very serious problem.
Kaplan notes that many clinicians are struggling with how to handle this emerging issue. Some people are promoting surveillance cultures on all patients who come in the hospital to see if theyre colonized and then put them into isolation; I dont think we really know what the right answer is, he says. The community strains are now circulating in many areas of the country in hospitals. Nosocomial staph infections, many of these are now the strains that are from the community MRSA isolates from the community are now being associated with hospitalacquired infections and Im sure this is going to increase with time.
Extended-spectrum beta-lactamases (ESBL)
Extended-spectrum beta-lactamases (ESBLs) are described as a rapidly-evolving group of beta-lactamases that are able to hydrolyze third-generation cephalosporins and aztreonam, but are inhibited by clavulanic acid.2 ESBLs provide a sobering illustration of the ability of gram-negative bacteria to develop new patterns of antibiotic resistance. There are currently a very limited number of options for antibiotic treatment of ESBL-producing organisms.
ESBLs arent getting as much attention, at least in the lay press, but theyre potentially as scary if not scarier organisms [than CAMRSA], Perl says. This actually can involve a group of gram-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 their significance in certain serious infections is vital in order to avoid treatment failures, according to Perl. The Clinical and Laboratory Standards Institute (CLSI) has developed guidelines for the detection of ESBLs produced by E. coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis. These guidelines recommend the use of K. pneumoniae ATCC 700603 (an ESBL producer) as a quality control organism in tests to detect the presence of ESBLs.3
What ICPs might be seeing are people who arent responding appropriately to therapy for gram-negative infections, Perl says. That requires education to make sure that people who are prescribers actually understand what an ESBL is. The other thing to say, and my perspective on MRSA and ESBLs is identical, is that again, this is an organism thats easily transmitted; it can be transmitted on hands just like MRSA and we should be identifying these people and isolating it. Im a firm believer that isolation in the healthcare setting for ESBLs is important, especially in high-risk settings like ICUs where its really easy for this to be transmitted from patient to patient.
Church notes that ESBLs were quite rare in her facility until about a year ago, when they began to increase in number. In our case they are primarily seen in urine cultures, and these are often in patients who have been exposed to multiple antibiotics because theyve got underlying conditions, she says. Many physicians didnt really understand what this was, so we have an electronic system here that we put in the computer where, once weve identified something, it will pop up again if theyre readmitted. The purpose of that is not so much just to designate the patient with an isolatable type of issue, but more to inform the physicians so they can know when they have to pay attention to the antibiotics they may need to talk to pharmacy or ID. Thats how we utilize it here.
Other Resistant Organisms
To me acinetobacter is one of the scariest ones thats out there, Perl says. Its a pathogen that really came into its own about three or four years ago in New York City where there was an outbreak that involved 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 resistant to everything except a drug called polymyxin B. That drug was developed in the 40s and I had never used it until last year. Its got a lot of associated toxicities with it. This is a pathogen that weve had in Baltimore since about 1995, and there are a lot of places that are seeing this.
Acinetobacter baumannii is a gram-negative bacillus that commonly colonizes aquatic environments. The organism is often cultured from hospitalized patients sputum or respiratory secretions, wounds, and urine. Acinetobacter can also be found in irrigating solutions and intravenous solutions. Infections often manifest as nosocomial pneumonia, infections associated with continuous ambulatory peritoneal dialysis, or catheter-associated bacteruria. Acinetobacter pneumonias often occur as outbreaks and are usually associated with colonized respiratory support equipment or fluids.4
It has an unbelievable ability to contaminate the environment much more so than MRSA, Perl continues. You have to throw out tons of equipment because you cant figure out where it is. Weve actually been criticized here because we have a pretty draconian approach to that organism we require oneon- one nursing and people signing in and out of rooms, but weve had no transmission since weve done that. The thing thats also concerning to me is that now as were getting more and more data, at least at our institution, that one of the sources of this is patients who come in from nursing homes and chronic ventilation facilities.
Hospital-acquired MRSA is, of course, still a significant concern as well. Church explains that, at her facility, studying MRSA in greater detail has proven to be beneficial. We had some work done here that showed our fluoroquinolone use was directly contributing to our increase in some MRSA we were seeing, so we revised some antibiotic prescribing habits in the ER to try and reduce that, she says. We did a study in 2002-2003 to try and understand where ours was coming in from. We looked at all the patients who were admitted to the clinical care unit for five months with active surveillance cultures and learned that the primary source of that was coming from residential facilities such as nursing homes, foster homes, and those types of institutions where you have large numbers of people living together.
As a result of these findings, Church says efforts were made to work with and educate staff at these types of facilities in order to promote hand hygiene. We still have some problems, but I think there have been some significant successes. In Oregon we have short lengths of stay, and that was offset by using our nursing homes and our rehabilitation centers, so when we began to see patients who were having surgery and coming back in with MRSA, and we didnt believe it had been acquired in the facility, we brought a lot of nursing homes together to take a look at what was going on and tell them what we were seeing from our side and determine what we could do to help them. That precipitated a number of changes that weve made, which I think have helped, but the education on the alcohol hand gels in particular, and good communication, were most important.
Ultimately, contending with antimicrobial-resistant organisms will continue to be a significant challenge for clinicians. The bugs are smarter than we are; theyll adapt and produce toxins and become resistant they will keep on adapting and were dealing with a more compromised population so well have new and evolving challenges, Perl says. I think the thing thats universal across all of these is that theres a very important role for very basic infection control and prevention strategies. I personally think that does involve surveillance.
Theres a very emotional debate thats going on right now in the infection control community about whether or not to do surveillance, and the whole concept of this is just the tip of the iceberg. Being extremely proactive and admitting that those bugs are there has really helped prevent transmission in our institution. The other thing to point out about it is that traditionally people thought it was the academic centers where all the resistance and bad bugs were created, but thats no longer true its very clear that theyre coming in from long-term care facilities, from the community, day care centers, and other places.
In addition to antibiotic resistance, communicable diseases are an ongoing concern for ICPs. From the apparent reemergence of certain diseases to decreases in vaccination rates in subsets of the population, the potential for an outbreak is always a concern for clinicians.
Pertussis (whooping cough) is one such condition that has received a seemingly increased amount of attention as of late. Were recognizing it more, probably because of better diagnostic techniques, Kaplan says. There may be some issues with regard to seeing it more because of waning immunity, especially in adolescents and older individuals, because now theres some pretty good evidence to show that its college-age people who are a reservoir for this organism. There are three or four studies now that show that if you have a college-age individual or an adult whos coughing for two or three weeks and its unexplained, pertussis is probably responsible for 25 percent of these cases.
Kaplan notes that it is difficult to make that diagnosis in older individuals. Diagnosis in children, however, has improved recently. In the past, you mainly had culture or fluorescent antibody testing, neither of which 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 proving that youve got a pertussis infection, he says. So its probably a combination of better diagnostics as well as some waning immunity, thus the recommendation for immunizing adolescents and adults with this new acellular pertussis vaccine.
Churchs community has seen pertussis outbreaks, and she says many adults thought they were protected from childhood vaccination. Learning that the vaccine wanes in its effectiveness over time was kind of a surprise to people. We also have areas where weve had difficulty 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 of the newer vaccine that can be given to adolescents and young adults will be extremely helpful.
In October 2005, three children in Minnesota were found to be infected with the polio virus. All members of the same family, which is part of the Amish community, the children had not been vaccinated against the disease. Minnesota Department of Health officials said the virus strain appears to be a variant of the one used in oral (live) polio vaccine. Before this version of the vaccine was discontinued in 2000, it caused approximately eight cases of paralytic polio per year in the United States. The current version is injected using a killed polio virus.
Dealing with outbreaks in populations that dont believe in vaccination can be extremely challenging for the healthcare community. If something starts in those populations then you have a whole group of people who are 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 methicillinresistant Staphylococcus aureus among professional football players. N Engl J Med. 2005 Feb 3;352(5):468-75.
2. Paterson DL, Bonomo RA. Extended-spectrum beta-lactamases: a clinical update.
Clin Microbiol Rev. 2005 Oct;18(4):657-86, table of contents.
3. Clinical and Laboratory Standards Institute. 2005. Performance standards for antimicrobial susceptibility testing. Fifteenth international supplement M100-S15. Clinical and Laboratory Standards Institute, Wayne, Pa.
Staying Vigilent Against TB
Some clinicians may have dismissed tuberculosis (TB) as qualifying as an emerging disease these days, but until it is completely eradicated, it remains a concern for public health officials.
Consider these facts from the World Health Organization (WHO):
- Someone in the world is newly infected with TB bacilli every second
- Overall, one-third of the worlds population is currently infected with the TB bacillus
- Five percent to 10 percent of people who are infected with TB bacilli (but who are not infected with HIV) become sick or infectious at some time during their life
TB is a contagious disease, and like the common cold, its transmission is airborne. When infectious people cough, sneeze, talk, or spit, they propel TB bacilli into the air; a person needs only to inhale a small number of these bacteria to be infected. Left untreated, each person with active TB disease will infect on average between 10 and 15 people every year. But people infected with TB bacilli will not necessarily become sick with the disease. The immune system walls off the TB bacilli which, protected by a thick waxy coat, can lie dormant for years. When an individuals immune system is weakened, the chances of becoming sick are greater.
Starting in the 1940s, scientists discovered the first of several medicines now used to treat TB. As a result, TB slowly began to decrease in the United States. But in the 1970s and early 1980s, the country let down its guard and TB control efforts were neglected. As a result, between 1985 and 1992, the number of TB cases increased. However, with increased funding and attention to the TB problem, there has been a steady decline in the number of persons with TB since 1992. But TB is still a problem; more than 14,000 cases were reported in 2003 in the United States.
Until 50 years ago, there were no medicines to cure TB. Now, strains that are resistant to a single drug have been documented in every country surveyed; strains of TB resistant to all major anti- TB drugs also have emerged. A particularly dangerous form of drug-resistant TB is multi-drug-resistant TB (MDR-TB), which is defined as the disease caused by TB bacilli resistant to at least isoniazid and rifampicin, the two most powerful anti-TB drugs. Rates of MDR-TB are high in some countries, and threaten TB control efforts.
The most important way to keep from spreading TB in a hospital setting is taking isolation measures with patients who are suspected or known TB carriers. Patients placed in isolation should remain in their isolation rooms with the door closed. To prevent the escape of droplet nuclei, the TB isolation room should be maintained under negative pressure. If possible, diagnostic and treatment procedures should be performed in the isolation rooms to avoid transporting patients through other areas of the facility. If patients who may have infectious TB must be transported outside their isolation rooms for medically essential procedures that cannot be performed in the isolation rooms, they should wear surgical masks that cover their mouths and noses during transport. Persons transporting the patients do not need to wear respiratory protection outside the TB isolation rooms. The number of persons entering an isolation room should be minimal. All persons who enter an isolation room should wear respiratory protection; the patients visitors should be given respirators to wear while in the isolation room, and they should be given general instructions on how to use their respirators. Personal respiratory protection should be used by persons entering rooms in which patients with known or suspected infectious TB are being isolated, persons present during cough-inducing or aerosol-generating procedures performed on such patients, and persons in other settings where administrative and engineering controls are not likely to protect them from inhaling infectious airborne droplet nuclei. Respiratory protective devices used in healthcare settings for protection against M. tuberculosis should meet the following standard performance criteria: the ability to filter particles 1mm in size in the unloaded state with a filter efficiency of greater or equal to 95 percent, given flow rates of up to 50L per minute; the ability to be qualitatively or quantitatively fit tested in a reliable 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 accordance with standards established by the Occupational Safety and Health Administration (OSHA) and good industrial hygiene practice, by HCWs each time they don their respirators.