(CNN) Global leaders met at the United Nationals General Assembly in New York Wednesday to address what experts are calling one of the biggest threats to global health: antimicrobial resistance.

It is only the fourth time in UN history that a health issue has been discussed at the assembly, after HIV, noncommunicable diseases such as obesity, and Ebola.

The high-level meeting on antimicrobial resistance saw heads of statecommit to address the issue, with 193 countries signing a landmark declaration that they will combat resistance and rid the world of "superbugs."

Drug-resistant bacteria are expected to kill 10 million people a year by 2050 -- that's one person every three seconds -- if nothing is done to solve the problem.

Here are five things you need to know about antimicrobial resistance.

1. What is antimicrobial resistance?

Antimicrobial resistance, commonly called AMR, is when bacteria, viruses, fungi and parasites become resistant to the drugs typically used to treat people infected by them. The drugs, which previously would have cured people of an infection, are no longer effective in killing the microbes. These resistant infections are often called superbugs.

"There are now many infections that cannot be treated at all," said Dr. Vicky Enne , a clinical microbiologist at University College London who is working on new diagnostics to better target prescriptions. "And the problem is becoming worse as the (microbes) are becoming more and more resistant."

Drugs once used to treat infections no longer work on a group of bacteria called Carbapenem-resistant enterobacteriaceae (CPE), which include common bacteria such as E. coli and Klebsiella pneumoniae. Others include methicillin-resistant staphylococcus aureus (MRSA), pseudomonas aeruginosa -- typically acquired in hospitals -- and gonorrhea. Enne notes that these infections can become severe if left untreated, leading to pneumonia, urinary tract infections, sepsis and death.

Infections such as HIV, tuberculosis and malaria are becoming increasingly untreatable because of antimicrobial resistance. Some infections require the use of older, more toxic antimicrobials as a last resort, but they're sometimes developing resistance even those drugs.

"It basically compromises the whole of modern medicine," she said.

2. Who is at risk?

Experts warn that everyone will be affected if nothing is done to address resistance as soon as possible.

Treating cuts and wounds could become problematic due to the risk of untreatable infection, and easy-to-cure infections such as gonorrhea will be rendered untreatable.

Childbirth and procedures such as cesarean sections, organ transplants, wound treatments and other forms of surgery will become high-risk as doctors lose access to antimicrobials that would normally protect patients from infection on the operating table.

The world will move back to a pre-antibiotic era, warned Enne.

For the moment, however, the people at most risk are those in the hospital, particularly those who are immunocompromised, such as chemotherapy patients, and are more likely to pick up one of these infections.

Another group at greater risk is residents of less-developed countries or countries with weaker health systems, as resistance is being reported in these regions more regularly. Enne highlights Asia and Southern Europe as places where untreatable cases have been reported, but adds that data are insufficient on the current situation in African countries.

For those in the West, infections can mostly still be treated in some way, but options are fast running out.

"If not action is taken, we'll see serious problems by the time our children grow up," said Enne.

3. Why has resistance developed?

There are many reasons underlying why resistance has emerged so widely among infectious microbes.

Some resistance happens naturally, due to underlying biology. The rapid replication rates of bacteria, viruses, parasites and fungi mean their turnover is high, and they are able to quickly evolve past a problem they encounter, such as a drug that is trying to kill them. The microbes that mutate and develop resistance to a drug will be the ones that survive and go on to proliferate the most.

But human behaviors and practices have helped these microbes evolve faster and more strategically than they otherwise may have, namely the widespread use of antimicrobials, offering more opportunity for the bugs to become resistant.

Among the problems: Antimicrobials are overprescribed and people buy them over the counter in certain countries. Drugs are shared, people don't finish courses of treatment and antibiotics are overused in veterinary practices. Another large-scale use of antimicrobials -- mostly antibiotics -- has been in farming, to promote animal growth. This is still standard practice in the United States and many parts of the world except the European Union, where these practices are banned.

Essentially, the widespread use of antibiotics -- in both humans and animals -- has helped microbes evolve to become resistant.

4. What can be done?

Enne says it's not too late to reduce the amount of resistance if individuals and governments alike commit to tackling the problem. "A lot of people aren't aware of the seriousness of it all," she said.

New antibiotics are needed to take the place of those that have been made redundant, but experts warn that this can take decades, so amending current practices is an immediate priority.

Photos: Disease vs. drugs: How microbes are winning the war Photos: Disease vs. drugs: How microbes are winning the war Experts warn that a global health crisis is on the horizon as drugs available for once treatable diseases are losing their edge. The bacteria, viruses and parasites behind diseases such as tuberculosis, malaria and gonorrhea are fighting back by developing resistance to our arsenal of pharmaceuticals.



With the World Health Organization saying that we could be heading to a "post-antibiotic age," what infections are becoming a concern?



Report by Meera Senthilingam Hide Caption 1 of 8 Photos: Disease vs. drugs: How microbes are winning the war Malaria (insert: Plasmodium falciparum)



Malaria was a target for global eradication in 1955 using the once potent drug chloroquine as the weapon of choice to kill the plasmodium parasites behind the disease. However, resistance to the drug developed and spread rapidly across the world rendering the drug, and hope of eradication, useless by the 1970s.



A new wave of excitement came soon after with the arrival of artemisinin, which is today prescribed as a combination therapy to avoid the development of resistance. Despite this strategy,

(insert: Plasmodium falciparum)Malaria was a target for global eradication in 1955 using the once potent drug chloroquine as the weapon of choice to kill the plasmodium parasites behind the disease. However, resistance to the drug developed and spread rapidly across the world rendering the drug, and hope of eradication, useless by the 1970s.A new wave of excitement came soon after with the arrival of artemisinin, which is today prescribed as a combination therapy to avoid the development of resistance. Despite this strategy, resistance has been reported in Cambodia and could once again spread globally. Globalization and increasing travel to remote locations means the 200 million cases of malaria estimated to occur each year are not just a concern for developing countries. Hide Caption 2 of 8 Photos: Disease vs. drugs: How microbes are winning the war HIV (insert: Human immunodeficiency virus)



The arrival of antiretroviral therapy changed the face of the HIV epidemic globally from a chronic, debilitating and inevitably fatal infection to one that can be managed to live a long and healthier life.



But the virus reproduces rapidly, meaning resistant forms could easily form and multiply. Up to 14% resistance was found in high-income countries soon after antiretrovirals were introduced in the 1990s and increased use of treatment in developing countries has seen resistance emerge more globally. In 2012, 35 million people were estimated to be living with HIV, based on World Health Organization reports, and with over 2 million people newly infected in 2012, HIV could one day return to pandemic levels if resistance continues to spread. Hide Caption 3 of 8 Photos: Disease vs. drugs: How microbes are winning the war Tuberculosis (insert: mycobacterium tuberculosis)



Tuberculosis almost disappeared in the majority of the Western world as countries developed. But the disease persists globally, with an estimated 8.6 million people developing TB in 2012 and 1.3 million dying from it.



The bacterium behind the disease, Mycobacterium tuberculosis, has developed not only multidrug resistant but also extensively drug resistant forms of the disease, which require an additional pool of more toxic drugs. In 2012, there were 450,000 cases of MDR-TB worldwide and XDR-TB was reported in 92 countries. (insert: mycobacterium tuberculosis)Tuberculosis almost disappeared in the majority of the Western world as countries developed. But the disease persists globally, with an estimated 8.6 million people developing TB in 2012 and 1.3 million dying from it.The bacterium behind the disease, Mycobacterium tuberculosis, has developed not only multidrug resistant but also extensively drug resistant forms of the disease, which require an additional pool of more toxic drugs. In 2012, there were 450,000 cases of MDR-TB worldwide and XDR-TB was reported in 92 countries. Countries such as India have reported patients with total resistance to all drugs. With few new drugs in the pipeline to control the bacteria, total resistance could spread. Hide Caption 4 of 8 Photos: Disease vs. drugs: How microbes are winning the war Typhoid Fever (insert: Salmonella typhi)



Immunization remains the weapon of choice in controlling typhoid fever. The disease still affects 21.5 million people in developing nations, and increased global travel means the disease is not limited to those countries. The United States sees over 5,000 people infected each year after consuming contaminated food and drink abroad.



The bacterium behind the disease, Salmonella typhi, can be killed with various antibiotics, but resistance is now arising to multiple antibiotics and complicating treatment, especially in South Asia, a popular holiday destination. Hide Caption 5 of 8 Photos: Disease vs. drugs: How microbes are winning the war Hospital acquired Infections (insert: Klebsiella)



Multidrug-resistant Staphylococcus aureus, which causes a range of symptoms from boils and abscesses to blood poisoning and arthritis, has been a concern for years in hospitals and whilst public health teams have been tackling it, a group of bugs known as the ESKAPE pathogens is taking the lead.



Standing for Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter, the ESKAPE pathogens cause a range of symptoms including pneumonia, urinary-tract infections, septicemia, meningitis and diarrhea. If resistance continues to rise, WHO reports highlight that a routine hospital visit could result in a more serious condition. Hide Caption 6 of 8 Photos: Disease vs. drugs: How microbes are winning the war Gonorrhea (insert: Neisseria Gonorrhoea)



Globally, there are an estimated 88 million cases of this sexually transmitted infection, caused by the bacterium Neisseria gonorrhoeae, each year. Resistance to antibiotics began to occur soon after their introduction in the 1930s and has continued to rise with resistance now seen against five of the drugs once used to treat it -- which include the commonly used antibiotics penicillin and tetracycline.



Only one class of drug, cephalosporins, remains with the ability to fight the bacteria, but resistance to this last resort has now occurred in 10 countries. If this spreads globally, gonorrhea could become untreatable and spread rapidly throughout a promiscuous population. Hide Caption 7 of 8 Photos: Disease vs. drugs: How microbes are winning the war Influenza (insert: influenza virus)

Influenza virus types A and B sweep through countries annually in the winter months; they cause fever, headaches and muscular pain in most cases, but also cause 3 million to 5 million cases of severe illness and 250,000 to 500,000 deaths each year, according to the WHO The antiviral drugs oseltamivir and zanamivir are the main means of fighting infection. Preventative antivirals amantadine and rimantadine were once used to control seasonal spread, but high levels of resistance means their use is no longer recommended.



The constantly evolving biology of the influenza virus means that resistance can easily form. Amantadine-resistant viruses began emerging in 2003 and oseltamivir-resistant viruses since 2007. Resistance to zanamivir has also been reported. While the majority of viruses found globally are still sensitive to the key drugs, the resistant forms could easily spread as no other drug options remain available. Hide Caption 8 of 8

What can individuals do? Wash your hands more regularly to avoid both contracting and spreading infections, especially when visiting people in the hospital.

You can also spread the word and help others become more aware. Ensure that you finish any course of antimicrobials prescribed to you, avoid sharing any drugs prescribed to you or buying any over the counter, and try to buy meat from farms that do not use antibiotics on their animals.

Also, if your physician doesn't think you need antibiotics, you probably don't. So just accept it. "People can help by not pressurizing their general practitioners for antibiotics," Enne said.

On a much larger scale, the solution will have to come from world leaders committing to end the problem, as they just have at the UN General Assembly, and creating policies and funds that support solutions.

The final report (PDF) from the Review on Antimicrobial Resistance , published in May, set out 10 recommendations to tackle resistance on a global scale by reducing unnecessary use, with a particular focus on four items: a global public awareness campaign, the supply of new antibiotics through increased research and development, improved diagnostic tests to ensure that antimicrobials are used only when needed, and reducing the unnecessary use of antibiotics in agriculture.

But all of this needs commitment and investment, stressed Enne, which is the goal of today's declaration.

"We've seen it addressed in various global forums. Hopefully, there will be willingness and investment from around the world," she said.

5. What are the consequences if nothing is done?

Today, superbugs are estimated to cause 700,000 deaths every year. If no action is taken as laid out, these numbers are expected to rise to 10 million deaths each year by 2050.

Join the conversation See the latest news and share your comments with CNN Health on Facebook and Twitter.

In addition to a basic lack of treatment for infections, many medical procedures will not be possible, adding to the number of possible deaths.

"Doctors won't be able to carry out life-saving procedures due to the risk of infection," Enne said.

In a statement supporting today's UN declaration, WHO Secretary-General Dr. Margaret Chan said, "antimicrobial resistance poses a fundamental threat to human health, development, and security."

If nothing is done, the last drugs standing will be knocked out of the game, and modern medicine will not be so modern.

"Antibiotics underpin the whole of modern medicine," Enne said, warning of the size of the challenge ahead. "It will be a considerable feat to solve the problem."