Tuesday, August 6, 2013

Rapid Diagnostics of Infectious Diseases in Hospitals

Infection Control Today recently provided an overview of hospital-acquired infections and the need to utilize rapid methods to screen for pathogens such as MRSA and influenza...

Hospitals constantly struggle to combat healthcare-acquired infections (HAIs). In recent years, the development and use of rapid diagnostic testing for these infectious diseases has helped to alleviate some of the issue, allowing healthcare providers to screen patients at the point of admission and take necessary precautions for carriers. Hospitals also want to know this information as quickly as possible in order to document infections. They do not receive additional payments for conditions that were not present at the time of admission, according to the Center for Medicare and Medicaid Services (CMS) website.

Tests are now available for bloodstream infections such as streptococcus and enterococcus as well as methicillin-resistant Staphylococcus aureus (MRSA) and respiratory illnesses including influenza A and influenza B.

In the past, diagnostic testing for these infections were primarily culture-based, meaning healthcare providers collected a sample  from the patient, put it on an agar plate, incubated the sample and then waited to see if bacteria grew out of it, says Paul Schreckenberger, PhD, professor of pathology at the Stritch School of Medicine at Loyola University and the director of the clinical microbiology lab for Loyola University Hospital. The entire process took about 24 hours to detect bacteria, at which point the lab would begin various tests to determine what bacteria was actually present. These tests could take another 24 hours to complete.

"They're labor-intensive and they're slow," Schreckenberger says of the old, culture-based tests. Physicians often relied on their clinical reasoning to diagnose certain illnesses such as influenza instead of waiting for the test results, he adds.

New molecular tests allow labs to look at the DNA in a specimen and determine the infection.

"Now we have these molecular techniques that completely revolutionized how testing is done, where we can take specimens, like nasal secretions, look for the DNA specimen and know within the hour whether it's a bacteria or virus and what bacteria or virus is present," Schreckenberger says.

During the flu outbreak this fall in Chicago, the rapid diagnostic testing allowed Loyola to identify the specific strand of influenza spreading throughout the city and determine that the flu vaccine covered that specific strand. This helped the city alert people to the potential harm and encourage them to get their shot, Schreckenberger says. "The information we're able to get is so influential in many ways, not just for the individual patient but to inform the masses what's going on, why is everybody getting sick, what's causing it and what's the solution," Schreckenberger explains.

The test Loyola uses to determine respiratory illness screens for 17 viruses and three bacteria, considered the most common causes of respiratory illnesses, which account for about 95 percent of all respiratory illness causes, Schreckenberger says.

Screening Upon Admission

Even as hospitals work to prevent HAIs, certain infections like Clostridium difficile (C. difficile) actually increased among pediatric patients and patients older than 85 years, according to a 2011 paper published in Laboratory Medicine. Screening patients at admission acts as one way to help combat these growing numbers, the article adds.

Common HAIs such as MRSA, vancomycin-resistant Enterococci (VRE) and C. difficile can and should be screened for prior to or at the time of admission, the paper states. Testing for these bacteria and infections at the point of admission allows the hospital to efficiently implement isolation if needed. Longer wait times for results leads to patients either being unnecessarily isolated or not isolated at all, in which case they risk transmitting the bacteria elsewhere and possibly infecting other patients, the article explains.

Loyola University Hospital screens every patient, regardless of his or her reason for admission, for MRSA during admission using a polymerase-chain reaction (PCR) test. Nurses swab new patients' noses, where the staph is carried, and send the sample to the lab where they test to see if the DNA of the sample matches the known DNA of infections.  In order to detect potential infections, the lab heats the DNA sample to separate the double-helix. Agents that match the DNA of a possible infection such as MRSA are added to the sample , where it tries to find a complementary strand on the patient's DNA. If it finds a match, it will bind with it to form a double helix. At this time, it begins multiplying until there are about 10 million strands, at which time it is measurable. The entire PCR amplification process takes about one hour, far quicker than the tests of years past.

Most patients don't know they carry MRSA because they are asymptomatic, Schreckenberger says, and for that reason he adds, "You come into our hospital you are going to have your nose checked."

Years of testing suggests that about 7 percent of the population acts as a carrier for MRSA. Loyola admits approximately 100 patients a day, meaning that seven of those patients will likely be a carrier, he explains.

Necessary Precautions

Screening for MRSA helps the hospital take precautions against the spread of the infection or contamination of the patient's room. Patients likely have wounds and stitches that make them more susceptible to infections post-surgery, Schreckenberger says.

If a patient carries staph, he or she may touch his or her nose, at which time the staph is transferred to his or her hands and skin and ultimately makes contact with the wound, increasing the risk of infection. People tend to think that the hospital gives them the infection, but it can be transmitted from your own body, Schreckenberger says.

"It's going to be infected from you, whatever you are carrying on your body," Schreckenberger explains. "If you get a urinary tract infection, it's not because you stood too close to somebody. You get a urinary tract infection because your own flora gets in your urine and causes infection."

Identifying the patients who carry staph allows the hospitals to stay one step ahead and take necessary precautions to prevent the infection. First, the healthcare providers need to alert the patient to their status as a carrier and explain to them simple ways they can aid in prevention, including frequent handwashing, Schreckenberger says. Second, the hospital can put an antibacterial ointment in the patient's nose that eliminates the staph. They can also provide the patient with special baths using antiseptic soap to disinfect any of the staph that may be on his or her skin. The patient will be placed in contact isolation, so that any healthcare provider or visitor to the room must wear gowns and gloves. Finally, the room will be cleaned somewhat differently once the patient leaves the hospital, Schreckenberger concluded.

"Maybe the patient who is a carrier never gets an infection. That's possible, but they still have the staph in their nose, so that staph is on their sheets, on their bedrail, on their remote control and on everything they touch in that room," Schreckenberger says. "Just knowing that they carry that organism is enough to initiate all of these steps."

Healthcare providers also need to be cautious about what they touch when caring for a carrier. Even with gloves on, the healthcare provider may touch the bedrail or a remote control that the patient previously touched and then touch another surface further contaminating it.

"There's a lot of touching that goes on in the room, and we don't know what we're leaving behind when we touch all of these things," Schreckenberger says.

For this reason, hospitals should make sure to thoroughly clean  these rooms upon a patient's discharge. Loyola brings in isolation carts for patients in contact isolation. These carts contain a remote control, stethoscope, blood pressure cuff—important equipment that may come in contact with the patient and potential staph. After discharge, the hospital removes the cart from the room and either discards or sanitizes these instruments elsewhere, Schreckenberger says. All surfaces in the room are then thoroughly cleaned.

"We take a lot of precautions that would not normally be done every day on every patient who doesn't have an infection," he adds.

Impact of Rapid Diagnostic Testing

Thanks to the rapid screening tests, Loyola reduced the number of MRSA infections at their hospital.

"We used to get about 90 of these infections a year," Schreckenberger says. "Now we average about 30 a year, so we had a two-thirds reduction in the number of these by screening patients, letting them know they are carriers and taking all of these precautions."

In the past, the culture-based tests sometimes gave false negatives because there weren't enough bacteria present to properly detect and identify the issue. The new tests, however, will only be positive in the presence of the agent of interest, Schreckenberger says, adding that these tests are better and more accurate than any previous test. "Because they are DNA-based they are very specific for the target that we're looking for," he says.

When selecting the right rapid diagnostic test for these infections, consider four key elements—flexible throughput, turnaround time, cost and assay content, the article from Laboratory Medicine suggests. Can you run one or more tests at a time without compromising results? If only one test can be administered at a time, how many instruments are needed to ensure an efficient lab and how much space is needed for these instruments? Can the test be completed in approximately two hours or less? What will the test cost the hospital and what will it cost the patient? Are the results unambiguous?

If tests meet these requirements, screening procedures, like the MRSA screening at Loyola, can play a key role in the prevention of HAIs. They alert physicians and other healthcare providers what patients carry the bacteria or virus at the time of admission. Knowing from the start that a patient carries the staph can help the hospital take necessary precautions to ensure that the patient does not develop an infection and the room does not become contaminated.

Tara Boyd is a freelance writer for ICT.

Reference: Centers for Medicare and Medicaid Services

Source: Infection Control Today (ICT) 


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