Sepsis happens when your body’s response to an infection spirals out of control and starts damaging your own organs. It doesn’t come from one specific germ or one type of injury. Any infection, anywhere in the body, can trigger it if the immune response becomes severe enough. In 2021, an estimated 166 million sepsis cases occurred worldwide, causing 21.4 million deaths, roughly 31.5% of all global deaths that year.
The Infections That Most Often Lead to Sepsis
Sepsis always starts with an infection, but some infections are far more likely to escalate than others. In adults, the breakdown looks like this:
- Lung infections (pneumonia): 35% of sepsis cases, making it the single most common trigger
- Urinary tract infections: 25%
- Gastrointestinal infections: 11%
- Skin and soft tissue infections: 11%
- Bloodstream infections: 5%
In children, the pattern shifts. Respiratory infections still lead at 29%, but gut infections jump to 24%, and bloodstream infections account for 13%. Urinary tract infections are less common in kids, making up only about 8% of pediatric sepsis cases.
What matters here is that most of these starting infections are ordinary. A UTI, a bout of pneumonia, an infected wound. Sepsis isn’t caused by exotic or rare diseases. It’s caused by common infections that, for various reasons, the body fails to contain.
What Happens Inside Your Body
When you get an infection, your immune system launches an inflammatory response to kill the invading germs. Normally, that response stays local: redness, swelling, and warmth around a wound, for instance. In sepsis, the response goes systemic, spreading through the entire bloodstream instead of staying at the infection site.
The process is more complicated than a simple overreaction. Your body fires off both pro-inflammatory signals (designed to kill pathogens) and anti-inflammatory signals (designed to limit tissue damage) at the same time. The pro-inflammatory side can cause collateral damage to your own organs. The anti-inflammatory side, while protective in some ways, can suppress your immune system enough to make you vulnerable to new, secondary infections. This dual response is why sepsis is so difficult to treat: the body is simultaneously attacking itself and leaving itself exposed.
The Germs Behind It
Bacteria cause the majority of sepsis cases, though viruses and fungi can trigger it too. The pathogens with the most sepsis-related deaths globally include E. coli, Klebsiella, Staph aureus, Pseudomonas, and Strep. E. coli has been the leading cause of bloodstream infections worldwide since 2005, though in the United States, Staph aureus holds the top spot. In European intensive care units, Klebsiella has overtaken E. coli as the most common cause of bloodstream infections from certain types of bacteria.
Fungal sepsis, most often caused by Candida species, tends to occur in people who are already hospitalized or have weakened immune systems. It’s less common than bacterial sepsis but carries a high mortality rate.
How Hospitals Create Risk
A significant portion of sepsis cases begin in healthcare settings, often because of invasive medical devices. Any tube or line that enters your body creates a direct path for bacteria to bypass the skin, your primary barrier against infection.
Breathing tubes are the most common culprit in intensive care, accounting for about 39% of device-related infections in one study of ICU patients. Urinary catheters follow at 19%, then feeding tubes at 18%, and central IV lines at 10%. An estimated 80,000 central line infections occur in ICU patients each year in the United States alone, and these infections carry a mortality rate as high as 25%.
Surgical sites also create entry points for bacteria. Any recent surgery, hospitalization, or severe illness raises your baseline risk because your body is already stressed and potentially immunocompromised.
Who Is Most Vulnerable
Sepsis can happen to anyone, but certain groups face substantially higher risk. Adults 65 and older account for the highest sepsis-related death toll: 9.28 million deaths globally in 2021. Children under one are also at elevated risk because their immune systems are still developing.
Chronic conditions increase vulnerability significantly. People with diabetes, lung disease, cancer, or kidney disease requiring dialysis are all at higher risk. About 1 in 5 sepsis hospitalizations are cancer-related. Anyone with a weakened immune system, whether from medication, illness, or organ transplant, is more susceptible because their body may not mount an effective early defense against infection.
Pregnancy and the postpartum period carry specific risks as well. Early rupture of membranes, cesarean delivery, infection of the uterine lining, or retained tissue from the pregnancy can all introduce or worsen infection. These conditions can escalate to sepsis quickly if not recognized.
Sepsis in Newborns
Newborns get sepsis through different routes depending on timing. Early-onset sepsis, occurring within the first 72 hours of life, is almost always transmitted vertically from the mother. Bacteria from the vagina or birth canal can ascend into the uterus and contaminate the amniotic fluid, reaching the baby’s bloodstream before or during delivery. The baby’s mucous membranes, lungs, or intestines can also be contaminated during passage through the birth canal.
Late-onset sepsis, appearing after the first week and up to 28 days of life, is typically picked up from the environment, often in hospital settings. Premature infants are especially vulnerable because they may have been exposed to bacteria in the uterus and their immune defenses are underdeveloped. Maternal risk factors for neonatal sepsis include prolonged rupture of membranes, infection of the membranes surrounding the fetus, and inadequate prenatal care.
How Sepsis Progresses
Sepsis exists on a spectrum, and it can move along that spectrum fast. The earliest stage looks like a systemic inflammatory response: fever above 100.4°F (or abnormally low temperature below 96.8°F), rapid heart rate above 90 beats per minute, and rapid breathing above 20 breaths per minute. These signs paired with a confirmed or suspected infection meet the basic definition of sepsis.
If the infection isn’t controlled, organs start to struggle. Blood pressure drops, and tissues stop getting enough oxygen. This is severe sepsis. When blood pressure stays dangerously low despite IV fluids, the condition becomes septic shock, the most life-threatening stage. The progression from early sepsis to shock can happen within hours, which is why speed of treatment matters enormously. Each hour of delay in appropriate care increases the risk of death.
The key warning signs to recognize are a combination of infection symptoms (fever, pain, cough, burning with urination) alongside unusual confusion, extreme fatigue, rapid breathing, or skin that feels clammy or looks mottled. Sepsis rarely announces itself with a single dramatic symptom. It’s the combination of “I have an infection” and “something feels very wrong” that should prompt immediate medical attention.