Carbapenem resistance and NDM-1: public health risks and prevention
Carbapenemases are enzymes, such as NDM-1, produced by some bacteria which cause destruction of the carbapenem antibiotics, resulting in resistance.
Carbapenems
Carbapenems are a powerful group of broad-spectrum antibiotics which are often our last effective defence against multi-resistant strains of bacteria like Klebsiella pneumoniae and Escherichia coli.
New-Delhi metallo beta-lactamase (NDM-1)
NDM-1 is an example of a type of enzyme called a carbapenemase (others include KPC, VIM, IMP and OXA-48 enzymes). Carbapenemases can destroy most penicillin-like antibiotics, even powerful carbapenems. The gene that encodes NDM-1 is often carried on pieces of bacterial DNA known as plasmids, which can be transferred between different bacteria. Although many types of bacteria can acquire this type of resistance, NDM-1 is most often seen in Klebsiella pneumoniae and E.coli.
When this resistance was first detected
The first case of a bacterial infection with this resistance was identified in January 2008. Monitoring of this resistance began in 2009 as more cases were identified.
Resistance to all types of antibiotics
Most bacteria with the NDM-1 enzyme remain susceptible to 2 antibiotics, neither of which is ideal for general use. These antibiotics are colistin (an old and rather toxic antibiotic) and tigecycline (a newer antibiotic than can only be used in some, not all types of infection). Otherwise bacteria with NDM are resistant to all antibiotics. A few isolates with NDM are completely resistant to antibiotics, including colistin and tigecycline.
How NDM-1 was named
The patient in whom this resistance was first identified contracted the resistant strain through travel to New Delhi, where they were hospitalised and first started showing symptoms. There is separate evidence that the NDM-1 resistance was already circulating in India in 2007.
It is common to name a new type of metallo beta-lactamase (ie antibiotic destroying enzyme) after the place where it is first identified, for example, another similar enzyme circulating in Brazil is named SPM (Sao Paulo Metallo) and another is VIM (Verona Imipenemase). The enzyme was originally named NDM-1 in a conference abstract in 2008. The NDM enzyme has now been reported in many parts of the world, including Australia, the USA, Holland, France, Sweden and Canada, with affected patients often having had prior hospital contact in the Indian subcontinent.
How this resistance began
The original evolution of this resistance was a random event - the escape of a gene from some unknown bacteria onto plasmid DNA that could move between bacteral species that are capable of causing infection. Subsequently it has probably been selected by heavy antibiotic use and has been allowed to spread among patients in these countries.
How infection is contracted
Cases of NDM-1 are more prevalent in the Indian subcontinent than elsewhere, and many of the cases that have been found elsewhere have a history of hospitalisation in the Indian subcontinent.
Some patients contract these resistant bacterial strains when they were in India, Pakistan or Bangladesh; they may be infected by the bacteria or may just become colonised (this means that they carry the bacteria harmlessly in their gut). Some needed emergency hospitalisation during travel, some were in poor health and divided their time and treatment between the UK and the Indian subcontinent, others travelled for medical tourism.
The risk to travellers
There appears to be minimal risk of infection to travellers to the Indian subcontinent who are not treated in hospital. If members of the public are travelling for surgery overseas they should satisfy themselves that appropriate infection control measures are in place.
How to prevent infection
Hospitals and healthcare professionals need to pay careful attention to the correct and appropriate use of antibiotics, ensure there is appropriate monitoring and surveillance of antibiotic resistance, and ensure appropriate infection control measures are in place.
To prevent spread of the resistant bacteria within hospitals it is important to practice good hygiene especially hand hygiene, and for healthcare professionals to use gloves and gowns where appropriate.
For advice on how hospital laboratories can detect carbapenem-resistant bacteria and prevent them from spreading, see the carbapenem resistance document collection.
The severity of this problem
The emergence of carbapenemases and carbapenem resistance is a major public health concern. The World Health Organization is emphasising this and the need for new antibiotics to be developed, and for countries to take action to combat antimicrobial resistance.
The danger of bacterial infections that have NDM-1
Infections have varied from being mild to potentially life threatening or fatal. The level of risk depends upon which part of the body is affected by the infection, and the general health of the patient.
The symptoms of bacterial infections that have NDM-1 or other carbapenemases
There are no common symptoms as the resistance can be expressed by a number of different types of bacteria, and symptoms vary with the site of infection. The bacteria cause opportunistic infections in hospital patients, with common sites of infection including: the blood, urinary tract, lungs, and wounds. The resistance makes the infections much harder to treat.