Most Common Healthcare-Associated Infections: 25 Bacteria, Viruses Causing HAIs

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Healthcare-associated infections continue  to trouble the healthcare industry. The Centers for Disease Control and Prevention estimates one in 20 patients will contract an HAI everyday, and some estimates suggest the economic burden of HAIs reaches $35.7 billion a year. Unfortunately for hospitals, they are a great breeding ground for infections. A lot of people — often with community-acquired infections — are grouped together in close quarters with suppressed immune systems, leaving patients highly susceptible to infection.

However, patient safety networks and organizations focused on quality are banding together to improve infection control and reduce the number of patients who contract these conditions.
Clostridium difficile, Staphylococcus aureus, norovirus, Escherichi coli. These are some of the better-known bacteria and viruses responsible for HAIs, yet many others exists that healthcare providers should be aware of as they work to eradicate these infections from their organizations.

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The following is a comprehensive list of 25 of the most common bacteria and viruses causing HAIs:

Acinetobacter baumannii
Outbreaks of the Acinetobacter bacteria are mainly found in intensive care units and areas with highly ill people, rarely occurring outside of healthcare settings. The bacteria pose little threat to healthy people, but patients with weakened immune systems and other comorbidities are more susceptible to transmission. The bacteria can cause blood infections, pneumonia, meningitis, urinary tract infections and wound infections, and are often resistant to commonly prescribed antibiotics. The bacteria gained the nickname "Iraqibacter" after exhibiting an extremely high presence in war-zone medical facilities in Iraq and Afghanistan and causing infections in wounded soldiers.

Bacteroides fragilis
B. fragilis is a normal bacteria found in the intestinal tract and the colon. However, it can cause infections, most commonly in cohort with other bacteria. While inherently resistant to penicillins, most antibacterial regimens can eliminate the infection. However, the bacteria's slow growth, increasing antimicrobial resistance and co-occurrence with other pathogens can make treatment more complicated.

Burkholderia cepacia
B. cepacia is a group of gram-negative bacteria. They generally prefer aquatic environments, often found colonized in intravenous solutions and irrigation systems in healthcare settings. The bacteria pose the highest threat to patients with chronic lung diseases, such as cystic fibrosis, and can lead to pneumonia due to suppressed lung health. B. cepacia are resistant to a number of antibiotics and can be spread via contaminated medications and medical devices, human to human contact or touching a contaminated surface.

Clostridium difficile
One of the most well-known HAIs, C. diff causes inflammation of the colon, and symptoms can range from diarrhea to life-threatening colitis. Antibiotic-associated diarrhea is the most common symptom, following medication ingestion that eliminates good bacteria from the intestine along with the bad. The bacteria are transmitted via the fecal-oral route, most commonly being transferred from an infection site to another patient by a healthcare provider's hands. C. diff is resistant to many routine cleaning products, including alcohol-based hand cleaners, so it is able to survive in clinical locations for extended periods of time. C. diff can usually be treated with antibiotics, but in some cases a stool transplant may help restore bacterial imbalances.

Clostridium sordellii
C. sordellii is a rare bacteria, most often causing infections in patients with underlying medical conditions. The bacteria can cause pneumonia, endocarditis, peritonitis and myonecrosis, and severe cases can lead to sepsis, though rarely. C. sordellii mainly affects women and is often linked to end of pregnancy, whether the pregnancy resulted in childbirth, abortion or spontaneous abortion. Its transmission route is still unknown.

Carbapenem-resistant Enterobacteriaceae
The Enterobacteriaceae bacteria family is infamous for its resistance to antibiotics, mainly carbapenem antibiotics, the class of antibiotics often used as a final line of defense against infections. Enterobacteriaceae are normally found in the gut but can cause serious infections if they travel to other parts of the body. CRE can be transmitted via human to human contact or coming in contact with an infected device, such as a catheter. The bacteria have the ability to innately break down carbapenems, rendering that class of antibiotic useless in infection control. CRE infections can have up to a 50 percent mortality rate.

Enterococcus faecalis
Another highly antibiotic-resistant bacteria, E. faecalis' resistance is inherent. The bacteria contain penicillin-binding proteins and are able to bypass folate synthesis, an important step in bacteria elimination. Recently, Enterococcus bacteria have acquired resistance to vancomycin, leaving just a few treatment options for patients. While the bacteria are normally found in the gut, they can cause infection when they spread, notably causing urinary tract infections, sepsis and wound infections. E. faecalis is a resilient bacteria, with the ability to survive in a temperature range of 50 degrees to 115 degrees Fahrenheit.

Escherichia coli
E. coli is another bacteria group commonly found in the gut but can also become pathogenic. It is the leading cause of urinary tract infections in hospitals, but can also cause gastroenteritis, pneumonia or even neonatal meningitis. The O157:H7 strain is commonly found as the source of infection in patients. Serious E. coli infections may lead to hemolytic-uremic syndrome, a disease that destroys red blood cells, causes acute kidney failure and reduces platelet counts. The E. coli bacteria have inhabited the earth for an estimated 20 million to 30 million years. E. coli is a very diverse bacteria — only 20 percent of its genome is found in all strains — and some researchers suggest it should be taxonomically reclassified.

Hepatitis A
The Hepatitis A virus is the least common of the three major Hepatitis viruses found in healthcare settings. The virus is spread through the fecal-oral route, and healthcare personnel are often infected when handling a patient in whom the infection is not yet recognized, is fecal incontinent or has diarrhea. The HAV vaccine is strongly recommended for children in the U.S. between their first and second birthdays, and it has proven to be extremely effective in community-acquired HAV infections.  

Hepatitis B
Hepatitis B can cause acute infections or chronic liver infections. An acute infection typically exhibits liver inflammation, vomiting and jaundice. Some acute cases can turn into chronic Hepatitis B, causing lifelong infection, cirrhosis, liver cancer, liver failure and death. HBV is typically spread through body fluids of an infected person being transmitted into a non-infected person, which in healthcare settings is often through contaminated needles, syringes or other sharps. The HBV vaccine is also highly effective, mostly when administered to children, as 95 percent develop protective antibodies. That protection percentage drops to 90 percent at age 40 and 75 percent for people age 65 and above.

Hepatitis C
Unlike HAV and HBV, there is no vaccine against HCV. While mainly transmitted through intravenous drug use in the community, the healthcare setting sees HCV transmission through contaminated syringes, needles or sharps, infected blood transfusions and sometimes even organ transplants that have not undergone adequate HCV screening. The U.S. implemented blood screening for HCV in 1992, before which blood transfusion was one of the major causes of infection transmission. Now, the risk is approximately 1 in 2 million units transferred. The majority of people diagnosed with HCV, 75 to 85 percent, will develop a chronic infection. In late 2013, the U.S. Food and Drug Administration approved two separate drugs for Hepatitis C treatment, Sovaldi and Olysio.

Human Immunodeficiency Virus
The HIV virus damages T cells that are vital in helping the body fight off diseases, leaving those infected at risk of many types of infections. Although HIV transmission in hospitals is rare, it is possible to be spread to patients via improper infection control procedures, such as sterilization and disinfection. HIV is transferred through bodily fluids, so healthcare personnel should take caution as they would with other bloodborne pathogens.

The influenza virus is a common one, but novel strains — strains not before seen in humans — and variant strains often emerge. The H1N1 strain, or swine flu, was one of the most recent deadly variants of the influenza A virus. The virus' ability to adapt into new strains causes researchers to have to update flu vaccines annually to reflect current influenza trends. While people often come down with the flu, in some severe cases it can lead to death.

Klebsiella pneumoniae
In the healthcare setting, Klebsiella bacteria, most often the pneumoniae species, cause urinary tract infections, wound infections, upper respiratory tract infections, osteomyelitis and even meningitis. The risk of infection heightens if a patient requires invasive medical devices, urinary catheters, ventilators and antibiotics. The Klebsiella genus has started developing antimicrobial resistance, causing treatment for such strains to be more limited. K. pneumoniae cannot be transmitted through the air, rather mainly through contact with an infected person. These bacteria are another that are normally found in the body but have the potential to cause infection. They cause approximately eight percent of HAIs in the U.S. and occur more frequently in premature infants and in the neonatal intensive care unit.

Methicillin-resistant Staphylococcus aureus
MRSA is an often-talked about HAI, often because its severe antimicrobial resistance makes it difficult to treat. Vancomycin has been used as treatment for MRSA, but now even vancomycin-resistant strains are emerging. MRSA infections generally appear on the skin, but they can spread to organs and into the bloodstream, causing sepsis, pneumonia and surgical site infections. The bacteria are spread through direct contact, usually through an open wound or contaminated hands. Proper hand hygiene is considered the best defense against MRSA transmission. Although MRSA remains a clinical threat to patients, studies report the rates of the bacteria are declining. The CDC reported a 54 percent decline in life-threatening MRSA infections from 2005 to 2011. Current research is examining the effect copper-infused hospital materials may have on eliminating MRSA, as copper alloys have demonstrated a 99.9 percent kill rate.

Morganella morganii
This bacteria is one of the less common HAIs, accounting for approximately one percent of nonsocomial infections, most often encountered in post-operative settings. It is associated with urinary tract infections, sepsis, pneumonia, inflammation of the eye and musculoskeletal infections. Although the M. morganii is naturally resistant to certain penicillins, it is still treatable with other antibiotics.

Mycobacterium abscessus
M. abscessus is a distant relative to the bacteria that cause tuberculosis and leprosy. Found in water, soil and dust, the bacteria are known to contaminate medication and medical devices. Most M. abscessus infections are of the skin or soft tissue under the skin, although it also can cause lung infections in people with chronic lung diseases. Transmission of the bacteria rarely occurs person to person, rather it is more commonly transferred via infected equipment or material in invasive medical procedures or when contaminated substances are injected into a patient.

The group of viruses known as norovirus is the most common cause of gastroenteritis. Healthcare facilities serve as optimal transmission spaces for the highly contagious virus, as the close quarters enable rapid person to person transmission. Some reports estimate it takes fewer than 20 norovirus particles to cause an infection. The virus exhibits strong survival outside of a human host, with some studies finding the virus persisting for weeks on hard surfaces, 12 days on fabrics and even months in still water. Proper hand hygiene is an effective way to avoid transmitting norovirus.

Psuedomonas aeruginosa
P. aeruginosa is one of the most common isolated pathogens in people hospitalized for more than one week. It thrives on moist surfaces, heightening the risk of infection for patients with catheters or ventilators. While treatable and curable with antibiotics, serious infections such as bacteremic pneumonia, sepsis, burn wound infections and meningitis from P. aeruginosa are linked to high mortality.

Staphylococcus aureus
S. aureus is a normal part of the skin flora, and approximately 30 percent of people carry the bacteria in their nose asymptomatically. However, the bacteria can be fatal in healthcare settings, especially when identified as the cause of sepsis, pneumonia, endocarditis or osteomyelitis. Improper hygiene protocol adherence is one of the biggest gateways for staphylococcus to be transmitted in the healthcare setting. The bacteria are increasingly becoming resistant to antibiotics, as evidenced by MRSA, which has evolved into its own separate concern area for healthcare personnel. Recently, researchers at the University of Iowa have developed a vaccine that, in animal model trials, has proven to be effective in providing sterilizing immunity from staphylococcus in infected organisms.

Stenotrophomonas maltophilia
S. maltophilia is very uncommon in humans, but its preferred aquatic habitat makes it a threat to patients requiring catheters, breathing tubes and intravenous fluids. In patients without compromised immune systems, S. maltophilia may cause pneumonia, urinary tract infections or sepsis, although the risk of infection is minimal without the presence of an invasive medical device. Immunocompromised patients may experience pulmonary infections as a result of colonized S. maltophilia bacteria. In many cases, removing the infected prosthesis is sufficient to treat the infection.

Mycobacterium tuberculosis
This bacteria, causing tuberculosis, is one of the leading causes of infection-caused mortality worldwide. In healthcare settings, especially in the U.S., the disease is not very common. However, it can be spread through the air from close contact to an infected person. M. tuberculosis organisms are, like all other HAIs, becoming resistant to antimicrobials, and drug-resistant tuberculosis is resistant to the first and second lines of best-treatment antibiotics.  

Vancomyin-resistant Staphylococcus aureus
Vancomycin-resistant S. aureus is another strain of staphyloccocus bacteria that has recently emerged as being resistant to vancomycin antibiotics. The bacteria were first discovered in 1997, but as of 2010, all vancomycin-resistant isolates have been eliminated by FDA-approved treatment regimens.  

Vancomycin-resistant Enterococci
The vancomycin-resistant strain of Enterococci bacteria can often be treated with other antibiotics. Patients may be infected with VRE via urinary catheters, in which case removing the catheter often is all that is required to eliminate the infection. VRE is not an airborne disease; rather, it is transmitted from person to person contact, so proper hand hygiene compliance and infection control are effective protocols in reducing the spread of this bacteria.

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