This Everyday Item is the Biggest Driver of Infectious Disease Outbreaks

Infectious diseases are disorders that are caused by germs or things like a bacteria, a virus, a fungus or a parasite.

Infectious diseases can range from mild to severe. Here are some common examples for each type:

1. Bacterial Infections

Strep throat: Caused by Streptococcus pyogenes bacteria.
Urinary tract infections (UTIs): Often caused by Escherichia coli.
Tuberculosis (TB): Caused by Mycobacterium tuberculosis.
Lyme disease: Transmitted through tick bites, caused by Borrelia burgdorferi.
Salmonella infections: From contaminated food or water.

2. Viral Infections

Influenza (Flu): Caused by influenza viruses.
COVID-19: Caused by the SARS-CoV-2 virus.
HIV/AIDS: Human Immunodeficiency Virus.
Common cold: Often caused by rhinoviruses.
Chickenpox: Caused by the varicella-zoster virus.

3. Fungal Infections

Athlete’s foot: Caused by Trichophyton fungus.
Yeast infections: Often caused by Candida albicans.
Ringworm: A skin infection caused by dermatophyte fungi.
Aspergillosis: Caused by Aspergillus molds, common in immune-compromised individuals.

4. Parasitic Infections

Malaria: Caused by Plasmodium parasites, transmitted by mosquitoes.
Giardiasis: A waterborne intestinal infection caused by Giardia lamblia.
Toxoplasmosis: Caused by Toxoplasma gondii, often from undercooked meat or cat feces.
Hookworm: Caused by parasitic worms that live in the intestines.

These diseases are typically spread through various means, including direct contact, contaminated food or water, insect bites, or respiratory droplets.

Organisms live in our bodies and are typically harmless, however, certain conditions may cause the organisms to spread infectious diseases that can be spread from person to person.

Some infectious diseases can be spread by insects or animals.

These health threats are called zoonotic infectious diseases, and recent outbreaks include COVID-19 and Ebola.

“In the age of COVID-19, it is understandable that many people may not realize how many outbreaks of other infectious diseases are caused by complex, intertwined ecological and socioeconomic conditions,” lead author Patrick Stephens, an associate research professor at the University of Georgia’s Odum School of Ecology in Athens says.

His team analyzed 4,400 zoonotic disease outbreaks worldwide since 1974. They identified the 100 largest, all of which infected thousands to hundreds of thousands of people. These were compared with 200 outbreaks that included 43 or fewer cases.

Causes of infectious diseases

1. Water

Contaminated water is the leading cause of large-scale outbreaks of infectious diseases that can be transmitted from animals to people, researchers say.

Water contamination was the most common cause of large outbreaks and the second most common cause of smaller ones. Examples of these water-associated diseases include hepatitis E, typhoid and dysentery.

Protect yourself from waterborne illnesses with the following tips from the CDC:

Flushing your faucets and showerheads if they have not been used recently
Cleaning, disinfecting, and maintaining all devices that use water
Communicating with your water utility if your water is brown or discolored or you notice a decrease in water pressure
Keeping private water sources safe
Checking with your building manager, owner or landlord to see what precautions they are taking to protect tenants from germs in the water

2. Viral pathogens

Large outbreaks are often driven by viral pathogens due to their high transmission potential and adaptability. Notable examples include SARS coronavirus, influenza virus, and Japanese encephalitis virus, each capable of rapid spread through respiratory droplets, vectors like mosquitoes, or direct contact.

These viral pathogens often lead to large outbreaks because of:

Human-to-human transmission: Respiratory viruses, like coronaviruses and influenza, can spread quickly in crowded environments.
Animal-to-human spillover: Many, like SARS-CoV and JEV, originate in animals and cross into human populations.
Lack of immunity: Novel viruses, such as SARS-CoV-2, face a population without prior exposure or immunity, leading to rapid spread.
Global travel: Facilitates the rapid movement of pathogens across borders.

3. Travel and zoonotic pathogens

“We know that factors like exposure to wild mammals, habitat disruption, international trade and travel and contact with contaminated food and water are important considerations,” Stephens said in a university news release.

“Perhaps two-thirds of future infectious disease outbreaks are expected to be caused by zoonotic pathogens, and the number of these diseases is growing worldwide,” he adds. “Our research is an extremely important first step to better understand global variation in the drivers of outbreaks.”

Smaller vs larger outbreaks

Smaller outbreaks are typically linked to localized factors such as food contamination, local livestock production, or direct human-animal contact. These events are often confined to specific regions and populations, arising from incidents like the spread of foodborne pathogens (e.g., Salmonella or E. coli), zoonotic diseases from livestock, or contamination during food processing.

In contrast, larger outbreaks often involve more diverse factors, such as highly transmissible pathogens, global travel, densely populated areas, or environmental changes that facilitate widespread spread. According to findings published in Philosophical Transactions B, large outbreaks are driven by a combination of viral, bacterial, or parasitic pathogens, with viral pathogens like SARS-CoV-2 and influenza playing a dominant role. Smaller outbreaks are generally more manageable but still require swift local interventions to prevent escalation.

Symptoms, treatment and prevention

Signs and symptoms of infectious diseases vary depending on the organism causing the infection, but often include fever and fatigue. Mild infections often respond to rest and home remedies. However, life-threatening infections may require hospitalization.

General signs and symptoms common to several infectious diseases include:

Fever
Diarrhea
Fatigue
Muscle aches
Coughing

Many infectious diseases, such as measles and chickenpox, can be prevented by vaccines. Frequent and thorough hand-washing will also help protect you from most infectious diseases.

When to see a doctor

If you experience any of the following, you should consult with your doctor:

Have been bitten by an animal
Are having trouble breathing
Have been coughing for more than a week
Have severe headache with fever
Experience a rash or swelling
Have an unexplained or prolonged fever
Have sudden vision problems

Medically Reviewed By:

Lisa Fitzpatrick

Dr. Lisa Fitzpatrick is a board-certified infectious diseases physician and medical epidemiologist with a background in public health. She is the founder and CEO of Grapevine Health, a digital health media company focused on improving patient engagement among Medicaid patients through culturally relevant health information.