Influenza infects up to a billion people worldwide each year

The flu is a contagious respiratory illness caused by influenza viruses

Unlike the common cold, influenza attacks suddenly with fever, body aches, and fatigue. Seasonal strains circulate worldwide, infecting up to a billion people each year and causing hundreds of thousands of deaths despite vaccines and treatments.

A novel H1N1 influenza strain sparked a 2009 global pandemic

First detected in Mexico, the 2009 “swine flu” pandemic infected up to 1.4B people worldwide. While mortality rates were lower than earlier pandemics, the outbreak still caused more than 150,000 deaths.

Why the 1918 flu killed between 50 and 100 million people

The 1918–1920 flu pandemic (once called, incorrectly, the Spanish flu) killed quickly and in huge numbers, with estimates of the global death toll ranging from 50 to 100 million people. Several factors contributed to the high mortality rate: lack of antibiotics, the global disruption of World War I, and more.

The 1957 and 1968 influenza pandemics caused millions of deaths worldwide

The 1957 H2N2 pandemic spread from East Asia, killing more than 1M globally, while the 1968 H3N2 pandemic began in Hong Kong and caused a similar toll, with both strains rapidly moving across continents.

Flu spreads through droplets in the air and on surfaces

Influenza passes mainly through tiny droplets released when sick people cough, sneeze or talk. The virus can also survive briefly on surfaces, allowing it to spread when others touch contaminated objects.

Annual flu shots remain the best defense against influenza

Flu vaccination typically reduces the risk of medical visits by 30 to 60% and lowers hospitalization rates by around 40%. Between 2023 and 2024, in the US alone, vaccines prevented an estimated 120,000 hospitalizations and nearly 7,900 deaths.

Human records of influenza stretch back more than two millennia

Accounts of flu-like illness appear as early as 412 BCE, when Hippocrates described a sudden wave of cough and fever. Centuries of recurring outbreaks culminated in the first clearly documented pandemic in 1580, spreading from Asia into Europe and Africa.

Find out how prevalent the flu is at this current moment

Updated weekly, this USAFacts resource shares current data from the CDC detailing how many cases of influenza and other flu-like illnesses accounted for doctor's visits. Monitor the spread of respiratory illness during flu season with this handy resource and prepare accordingly.

Fungal diseases cost the US around $19B annually

Estimates derived from health insurance claims, death certificates, and hospitalization data suggest that fungus is a significant medical issue. Each year, fungal diseases kill some 7,300 people—roughly the same number of deaths attributed to motor vehicles striking pedestrians. Around 130,000 people are hospitalized with fungal diseases, and the total national cost from fungal diseases is estimated to be about $19B—a figure that roughly matches Jamaica's entire gross domestic product.

Learn the history and science of influenza in 'This Podcast Will Kill You'

In their flu episode, cohosts Erin Welsh and Erin Allmann Updyke unpack influenza’s biology, history, and impact—explaining everything from past pandemics to modern vaccines, all with their trademark mix of science and storytelling.

More than 4,000 people died from cholera in 2023

This global health threat sickened more than half a million people in 2023 and killed 4,007 people. That's a 71% increase in deaths as compared to a year earlier. (Report only offered in PDF format.)

West Nile was reported in 47 states in 2025, with more than 1,400 people severely affected

Tracking numbers from the CDC indicate that the virus spread widely that year, with more than 2,000 reported human cases and many states seeing more than 25 sickened people. More than 1,400 people had neuroinvasive cases of the disease—meaning the virus had entered the nervous system, which can cause severe, potentially life-threatening illness.

1 in 6 Americans get food poisoning each year

The US federal government estimates there are about 48 million cases of foodborne illness in the country annually, resulting in as many as 3,000 deaths and 128,000 hospitalizations. Food poisoning puts those with weakened immune systems, the elderly, pregnant people, and young children at particularly high risk. This chart of common disease-causing pathogens highlights common threats and details about them, including likely food sources.

Antimicrobial resistance is responsible for 1.3 million deaths each year

Antimicrobial resistance is a global health threat, driven by the misuse and overuse of antimicrobials in humans, animals, and more. Estimates suggest superbugs could lead to $1T in healthcare costs by 2050, and the world faces a shortage of new drug development to meet the challenge.

Mosquitoes top the ranking of the world's deadliest animals

Mosquitos kill about 760,000 people every year. The vast majority of those deaths are caused by malaria, which is transmitted and spread by the Anopheles mosquito. The second-place deadliest animal title goes to snakes, with an estimated human death toll of around 100,000 annually.

Estimates suggest inactivity contributes to 6% of deaths worldwide

The World Health Organization identifies physical inactivity as the fourth leading modifiable risk factor for global mortality, just behind hypertension, tobacco use, and high blood glucose. Latest estimates are that inactivity contributes to 6% of deaths and significantly increases the burden of chronic diseases like heart disease, diabetes, and cancer.

Hand, foot, and mouth is usually seasonal—peaking in summer—but not always

This painful, contagious disease most commonly has outbreaks in summer and early fall in the US because the enteroviruses that cause disease can most readily survive and be transmitted in warmer, humid conditions. It can still show up throughout the year, however.

More than 200,000 people are diagnosed with leprosy annually

The disease still occurs in more than 120 countries. Brazil, India, and Indonesia continue to report more than 10,000 new cases annually.

See the polio cases that occur worldwide each year by region

Worldwide, the number of cases of polio reported each year from 1980 to 2024 has declined. This graphic depicts regional trends and declines by year.

As of 2022, scientists estimate that 117 billion people have been born on Earth

Although no demographic data exist for more than 99% of the time humans have existed, this value can be estimated by tracking approximate population sizes over different periods and the birth rates within those periods. In 2022, about 6.8% of humans that have ever been born were alive.

See how Ebola tore through Guinea, Sierra Leone, and Liberia in 2014-2016.

There have been close to 40 Ebola outbreaks since 1976

Ebola is a rare but deadly virus that causes severe illness, organ damage, and sometimes internal bleeding. It spreads through contact with infected bodily fluids and is most common in parts of sub-Saharan Africa. This explainer covers its symptoms, transmission, and treatment options.

Cryptococcus neoformans, a growing threat, causes infections in the brain and lungs

This inhalable, microscopic pathogen is found worldwide. It rarely causes illness, but it can take root in those with compromised immune systems, including people with advanced HIV/AIDS. Symptoms of cryptococcal infection—such as a stiff neck, vomiting, and confusion—can begin weeks or months after breathing in spores, though sometimes symptoms won’t appear for years. There are no known cases of transmission between people or between people and animals.

Measles symptoms range from fever to pneumonia and encephalitis

While less common, most measles-related deaths come from secondary conditions such as pneumonia (one to six cases per 100 patients) and encephalitis (one case per 1,000 patients). Blindness, which is rare, may arise from corneal ulceration.

World health experts expect more than 240 million global cases of AMD in 2030

The World Health Organization estimated in 2019 that by 2020 there would be roughly 195.6 million cases of age-related macular degeneration and projected that the number would continue to grow. (Some users may experience a paywall.)

Roughly 1 in 5 cancers are caused by viruses

About 20% of cancers are caused by viruses, with seven specific oncoviruses causing between 10% and 15% of cancers worldwide. These include human papillomavirus and hepatitis B and C viruses, which can lead to diseases such as cervical and liver cancer. Understanding the mechanisms of these viruses is crucial for prevention and treatment strategies.

11 people died from firework injuries in the US in 2024.

Human-to-human transmission of hantavirus remains extremely rare, so the 2026 hantavirus cruise ship outbreak doesn't mean we're facing a COVID-style pandemic risk.

About 12.5% of US adults experience a phobia in their lifetime, a diagnosis that hinges on the intense fear interfering with daily life and persisting for at least six months.

Volcanic activity may have triggered the Black Death by spewing gases that led to crop failures in Europe, thus forcing the import of grain ships with plague-infested fleas.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

In 2026, Finland was named the world's happiest country for the ninth consecutive year based on its wealth, social safety network, and high life expectancy, among other factors.

The deadliest aspect of volcanic eruptions is often not lava, but pyroclastic flows—avalanches of ash, gas, and rock that can move more than half the speed of sound.

Poison ivy can cause rashes year-round since all parts of the plant contain urushiol, the oil that triggers our allergic response.

The Russia-Ukraine conflict is the largest ground war in Europe since World War II in casualties, forces mobilized, and displacement of civilians.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

Take a 3D tour of the Hajj, Islam's annual pilgrimage to Mecca, undertaken by more than 1.5 million Muslims each year.

Roughly 43 million US borrowers owe roughly $1.7T in student debt, the second-largest source of consumer debt behind mortgages.

About 2,000 US babies are born annually without some portion of their limbs, potentially leading to a lifetime of pricey prosthetics.

Up to a million Girl Scouts sell about 200 million cookie boxes every spring, generating $800 million, largely because refusing a child is frowned upon

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

US intelligence allegedly pursued more than 600 schemes to assassinate Cuban revolutionary Fidel Castro.

Telehealth demand for GLP-1s for weight loss is booming as consumers seek easier access.

Elk Cloner, the first computer virus to spread in public, was written as a practical joke by Richard Skrenta, a Pittsburgh high school student.

The most expensive ad of all time was for Chanel No. 5 perfume and cost roughly $33M to produce in 2004—about $57M in today's dollars.

Electrical grids worldwide must double their power delivery capacity by 2050 to meet surging demand from AI and electric vehicles.

An initial public offering or 'IPO' is the process of a private company becoming public by putting shares of the company on the stock market for purchase.