Yes, you can have sepsis without a fever. In fact, it’s surprisingly common. In one study of 378 patients with septic shock, 45% had no fever at all, whether measured in the emergency department or reported by the patient. Some sepsis patients even develop an abnormally low body temperature. The absence of fever does not mean the infection is less serious. It often means the opposite.
How Common Is Afebrile Sepsis?
Many people assume that a dangerous infection will always cause a high temperature, but sepsis breaks that rule regularly. Nearly half of septic shock patients in emergency departments present without a fever above 100.4°F. Some arrive with a normal temperature, while others are hypothermic, meaning their body temperature has dropped below the normal range.
This matters because fever is one of the most visible red flags that prompts both patients and healthcare providers to suspect infection. When it’s missing, sepsis can go unrecognized longer, delaying treatment. Research in both adults and children has shown that a normal or low body temperature in the emergency department can slow the clinical response, simply because the absence of fever lowers the perceived urgency.
Why Some People Don’t Develop a Fever
Fever is generated by your immune system’s inflammatory response. When your body detects an infection, immune cells release signaling molecules that raise your internal thermostat. In some sepsis patients, this inflammatory cascade is blunted or overwhelmed by an opposing anti-inflammatory response. The result: your body fights the infection without ever turning up the heat.
There’s also a vascular explanation. Sepsis can cause widespread damage to the lining of blood vessels, leading to abnormal dilation and heat loss through the skin. If your body can’t constrict surface blood vessels to trap warmth, your core temperature may drop instead of rising. People with underlying cardiovascular disease may be especially vulnerable to this because their circulatory system is already less able to make the rapid adjustments needed to maintain temperature, like increasing heart rate or redirecting blood flow from the skin to deeper tissues.
Who Is Most Likely to Have Sepsis Without Fever
Certain groups are more prone to afebrile sepsis. Older adults are at the top of the list. Aging weakens the immune system’s ability to mount a full inflammatory response, so elderly patients with serious infections frequently present with confusion or low blood pressure rather than a high temperature.
People who are immunocompromised, whether from chemotherapy, organ transplant medications, long-term steroid use, diabetes, or autoimmune conditions, also tend to show atypical symptoms. Their immune systems are less capable of generating the normal signs of infection, and standard diagnostic tests may return results that look less alarming than the actual severity warrants. Very young infants are another high-risk group, as their temperature regulation and immune responses are still immature.
Afebrile Sepsis Carries Higher Risk
Not only can sepsis occur without fever, but the absence of fever is linked to worse outcomes. In a study comparing febrile and afebrile patients with severe sepsis, the 28-day mortality rate was 37.5% in patients without fever compared to 18.2% in those who had a fever. ICU mortality followed the same pattern: 29.2% for afebrile patients versus 11.4% for febrile patients.
Afebrile patients also spent more time in the hospital (a median of 12.6 days compared to 8.3 days) and were more than twice as likely to develop secondary infections, meaning new infections acquired during their hospital stay. The inability to mount a fever appears to reflect a deeper immune dysfunction that leaves the body less equipped to contain the original infection and more vulnerable to additional ones.
How Sepsis Is Identified Without a Temperature Spike
The current medical definition of sepsis does not require a fever. The most widely used framework, known as Sepsis-3, defines sepsis as life-threatening organ dysfunction caused by a harmful immune response to infection. Diagnosis centers on signs of organ failure, not on any single vital sign like temperature.
A bedside screening tool called qSOFA helps identify patients at risk. It uses three criteria: a respiratory rate of 22 breaths per minute or higher, a systolic blood pressure of 100 mmHg or lower, and altered mental status (any change in alertness or confusion). If two of these three are present in someone with a suspected infection, the risk of a poor outcome rises significantly. Notice that temperature is not part of this tool at all.
Older screening criteria, known as SIRS, did include temperature as one of four factors, but the international task force that developed Sepsis-3 unanimously agreed that relying on SIRS criteria was unhelpful for identifying sepsis. Too many patients with sepsis didn’t meet those older thresholds, and too many patients without sepsis did.
Signs to Watch For Beyond Fever
If fever isn’t reliable, what should you watch for? The most important warning signs of sepsis overlap with the qSOFA criteria but also include symptoms you can notice at home:
- Confusion or unusual drowsiness: Any change in mental sharpness, difficulty staying awake, or disorientation can signal that organs, including the brain, aren’t getting enough blood flow.
- Rapid breathing or shortness of breath: Breathing faster than normal at rest, especially when combined with other symptoms, is a key early indicator.
- Low blood pressure or dizziness: Feeling lightheaded when standing, or a measured blood pressure drop, suggests the cardiovascular system is struggling.
- Rapid heart rate: A pulse that stays elevated even when you’re resting.
- Cold or clammy skin: Particularly in someone who is known to have an infection, cool and mottled skin can indicate poor circulation.
- Very low urine output: Producing much less urine than normal is a sign that the kidneys may be affected.
These signs are especially important in people who are elderly, immunocompromised, or already being treated for an infection that doesn’t seem to be improving. A normal temperature in the presence of these symptoms should raise concern, not provide reassurance.
How Blood Tests Help Confirm Sepsis
When sepsis is suspected, blood tests can help confirm it regardless of whether a fever is present. Lactate levels measure how well oxygen is reaching your tissues. Elevated lactate suggests your organs are under stress. Procalcitonin is another marker that rises in response to bacterial infection. Levels above 2.0 ng/mL at ICU admission are associated with a significantly higher risk of severe sepsis or septic shock compared to levels below 0.5 ng/mL. White blood cell counts, either unusually high or unusually low, also provide clues.
No single blood test confirms sepsis on its own. Clinicians use these results alongside vital signs, physical examination, and the overall clinical picture. The key takeaway is that none of these diagnostic tools depend on the patient having a fever. Sepsis is fundamentally about organ dysfunction, and the tools used to detect it reflect that.