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Staphylococcus aureus is a gram positive bacteria which shows high resistance to antibiotics. There are two variants of Staphylococcus aureus depending on the resistance shown by them to the antibiotic methicillin. MRSA (methicillin resistant Staphylococcus aureus) is a variant of the species which shows resistance to methicillin antibiotics belonging to the penicillin group of antibiotics, The other variant, which is susceptible to it, is known as methicillin susceptible Staphylococcus aureus.
MRSA is localized in the nares, skin and the mucosa of the vagina and rectum. MRSA is a major problem in the health care setting as it is a predominantly hospital acquired infection but it is increasingly becoming a community problem as well. This article gives an overview on the MRSA rapid test and the importance of MRSA rapid test verification.
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What is the Rapid MRSA Test?
Traditionally available methods like culture can differentiate between the two variants of staphylococcus aureus in 24 to 48 hours or longer and it may take days to confirm positives.
A new rapid test has been devised which can give the result in 2 hours. This test is known as the MRSA rapid test. It is manufactured by different companies. It is available under the brand name of BD GeneOhm StaphSR assay. The product's manufacturer is BD (Becton, Dickinson and Co.).
This test assesses the blood sample of the patient for the genetic material specific for these two main forms of the bacteria.
It is also available under the name of 3M BacLite Rapid MRSA Test. This test measures the activity of an enzyme, adenylate cyclase which regulates energy provision in staphylococcus aureus. This test gives results within 5 hours. It is a highly sensitive rapid culture based screening test. In this test, nasal or groin swabs are used. Nasal swabs have a diagnostic sensitivity of 94.6% and a specificity of 96.9%. Groin swabs have a sensitivity of 95.9% and a specificity of 88.8%.
This test is used to differentiate MRSA from the methicillin susceptible variant of Staphylococcus aureus so that depending on the susceptibility of the bacteria, antibiotics can be prescribed.
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Why is MRSA Rapid Test done?
According to FDA recommendations, this test should be used in patients who are suspected to have a Staphylococcus aureus infection. But it should not be used to monitor treatment or to initially detect the infection. Though follow up testing is necessary by physicians to ultimately decide the proper antibiotic for treatment, this test will give a fair idea of what will be effective by narrowing down choices. It should be used for the very sick hospitalised patients having highly critical infections. But it may eventually be used in the community setting as well in less critical infections.
There are many advantages of this test:
- It interrupts MRSA spread which is a highly resistant organism.
- It reduces the unnecessary use of broad spectrum antibiotics.
- It prevents the emergence of new resistant organisms.
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What do the results of MRSA Rapid Test mean?
A positive MRSA Rapid Test means that the patient is infected with MRSA and thus the necessary and effective antibiotics against it should be instituted. A negative test means that the bacteria is methicillin sensitive and hence antibiotics should be given accordingly.
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Importance of MRSA Rapid Test Verification
Verification of the results requires the time consuming antibiotic susceptibility testing. This test determines the antibiotic to which the MRSA is susceptible.
The importance of MRSA Rapid Test Verification is due to the following reasons:
- Proper antibiotics are prescribed to control the infection and prevent MRSA spread.
- Sometimes false negative and false positive results can occur with these rapid screening tests and hence verification is necessary so that unnecessary antibiotics are not prescribed and at the same time, the infection is not missed out.
- It is necessary to confirm the antibiotic to which the MRSA is susceptible so that proper treatment can be given.
- Improper use of antibiotics can lead to emergence of new resistant organisms.
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Refereces and Further Reading
- Rapid MRSA Test gets FDA OK
- Superbug: The Fatal Menace of MRSA by Maryn McKenna
- Updates in diagnostic pathology by David C. Chhieng, Gene Philip Siegal
- Staphylococci in Human Disease by Kent B. Crossley, Gordon Archer, Kimberly Jefferson, Vance Fowler
- Methicillin-resistant Staphylococcus aureus (MRSA) protocols, Volumes 390-391 by Yinduo Ji