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Antimicrobial resistance

Fact sheet N°194
Updated May 2013


Key facts

  • Infections caused by resistant microorganisms often fail to respond to conventional treatment, resulting in prolonged illness, greater risk of death and higher costs.
  • Tuberculosis strains resistant to isoniazid and rifampicin (multidrug-resistance - MDR-TB) require treatment courses that are much longer and less effective. WHO estimates that there are about 630 000 MDR-TB cases in the world.
  • Resistance to earlier generation antimalarial medicines such as chloroquine and sulfadoxine-pyrimethamine is widespread in most malaria-endemic countries.
  • A high percentage of hospital-acquired infections are caused by highly resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) or multidrug-resistant Gram-negative bacteria.
  • New resistance mechanisms have emerged, making the latest generation of antibiotics virtually ineffective.

What is antimicrobial resistance?

Antimicrobial resistance (AMR) is resistance of a microorganism to an antimicrobial medicine to which it was originally sensitive. Resistant organisms (they include bacteria, fungi, viruses and some parasites) are able to withstand attack by antimicrobial medicines, such as antibiotics, antifungals, antivirals, and antimalarials, so that standard treatments become ineffective and infections persist increasing risk of spread to others. The evolution of resistant strains is a natural phenomenon that happens when microorganisms are exposed to antimicrobial drugs, and resistant traits can be exchanged between certain types of bacteria. The misuse of antimicrobial medicines accelerates this natural phenomenon. Poor infection control practices encourages the spread of AMR.

Why is antimicrobial resistance a global concern?

AMR kills

Infections caused by resistant microorganisms often fail to respond to the standard treatment, resulting in prolonged illness and greater risk of death. The death rate for patients with serious infections treated in hospitals is about twice that in patients with infections caused by non-resistant bacteria.

AMR hampers the control of infectious diseases

AMR reduces the effectiveness of treatment, thus patients remain infectious for a longer time, increasing the risk of spreading resistant microorganisms to others.

AMR threatens a return to the pre-antibiotic era

Many infectious diseases risk becoming untreatable and uncontrollable, which could derail the progress made towards reaching the targets of the health-related United Nations Millennium Development Goals set for 2015.

AMR increases the costs of health care

When infections become resistant to first-line medicines, more expensive therapies must be used. The longer duration of illness and treatment, often in hospitals, increases health-care costs and the economic burden to families and societies.

AMR jeopardizes health-care gains to society

The achievements of modern medicine are put at risk by AMR. Without effective antimicrobials for care and prevention of infections, the success of treatments such as organ transplantation, cancer chemotherapy and major surgery would be compromised.

AMR threatens health security, and damages trade and economies

The growth of global trade and travel allows resistant microorganisms to be spread rapidly to distant countries and continents through humans and food.

Facts on antimicrobial resistance

In 2011 there were an estimated 630 000 cases of MDR-TB among the world’s 12 million cases of TB. Globally, 3.7% of new cases and 20% of previously treated cases are estimated to have MDR-TB, with substantial differences in the frequency of MDR-TB between countries. Extensively drug-resistant TB (XDR-TB, defined as MDR-TB plus resistance to any fluoroquinolone and any second-line injectable drug) has been identified in 84 countries globally.

Percentage of MDR-TB among new TB cases since 1994

A high percentage of hospital-acquired infections are caused by highly resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycinor multidrug-resistant enterococciGram-negative bacteria .

Staphylococcus aureus (hospital isolates): percentage of methicillin-resistant strains, 2007, Latin America and the Caribbean

Ciprofloxacin is the only antibiotic currently recommended by WHO for the management of bloody diarrhoea due to Shigella organisms, now that widespread resistance has developed to other previously effective antibiotics. But the rapidly increasing prevalence of resistance to ciprofloxacin is reducing the options for safe and effective treatment of shigellosis, particularly for children.

AMR has become a serious problem for treatment of gonorrhoea (caused by Neisseria gonorrhoeae), involving even "last-line" oral cephalosporins, and is increasing in prevalence worldwide. Untreatable gonococcal infections would result in increased rates of illness and death, thus reversing the gains made in the control of this sexually transmitted infection.

New resistance mechanisms, such as enzymes produced by the bacteria that destroy last generation antibiotics, have emerged among several Gram-negative bacilli and have rapidly spread to many countries. This can render ineffective powerful antibiotics, which are often the last defense against multi-resistant strains of bacteria. This new resistant mechanism is encountered in ordinary human pathogens (e.g. Escherichia coli) that causes common infections such as urinary tract infection.

Resistance to earlier generation antimalarial medicines such as chloroquine and sulfadoxine-pyrimethamine is widespread in most malaria-endemic countries. Falciparum malaria parasites resistant to artemisinins are emerging in South-East Asia; infections show delayed clearance (meaning that the parasite remains in the blood for longer), after the start of treatment and increased morbidity and mortality.

Percentages of patients with P. falciparum parasitaemia on day 3 after treatment with an ACT (2006–2010)

Resistance is an emerging concern for treatment of HIV infection, after the rapid expansion in access to antiretroviral medicines in recent years; national surveys are underway to detect and monitor resistance.

Because of the constantly evolving nature of influenza, resistance to antiviral drugs is continuously emerging. By 2012, virtually all circulating A viruses in humans were resistant to amantadine and rimantadine, while the frequency of resistance to the neuraminidase inhibitor oseltamivir remains low (1-2%) and no resistance to zanamivir has been detected. Antiviral susceptibility is monitored through the WHO Global Surveillance and Response System.

What accelerates the emergence and spread of antimicrobial resistance?

The development of AMR is a natural phenomenon. However, certain human actions actually accelerate the emergence and spread of AMR. AMR is a complex problem driven by many interconnected factors so single, isolated interventions have little impact and coordinated actions are required.

Underlying factors that accelerate the emergence and spread of AMR include:

  • lack of a comprehensive and coordinated response;
  • weak or absent antimicrobial resistance surveillance and monitoring systems;
  • inadequate systems to ensure quality and uninterrupted supply of medicines;
  • inappropriate use of antimicrobial medicines, including in animal husbandry;
  • poor infection prevention and control practices;
  • insufficient diagnostic, prevention and therapeutic tools.

WHO's response

WHO is guiding the response to AMR through:

  • fostering coordinated actions by all stakeholders;
  • creating policy guidance, support for surveillance, technical assistance, knowledge generation and partnerships;
  • fostering innovation, research and development.

WHO calls on all key stakeholders, including policy-makers and planners, the public and patients, practitioners and prescribers, pharmacists and dispensers, and the pharmaceutical industry, to act and take responsibility for combating antimicrobial resistance.

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