What causes high fever with no other symptoms? Discover the causes of Fever of Unknown Origin (FUOs) and how to manage them.

Understanding Fever of Unknown Origin (FUOs)

Fever is a common occurrence, often indicating the body’s response to an illness or infection. However, in some cases, a high fever may not be accompanied by any other obvious symptoms, leading to a condition known as Fever of Unknown Origin (FUOs). This article explores the causes, symptoms, and management of FUOs, providing a comprehensive overview for healthcare professionals and individuals alike.

Causes of Fever of Unknown Origin (FUOs)

There are several potential causes of FUOs, including:

• Infectious Diseases: A variety of bacterial, viral, fungal, and parasitic infections can lead to FUOs, such as tuberculosis, endocarditis, and malaria.
• Certain Medications: Some medications, such as antibiotics and antidepressants, can cause fever as a side effect.
• Heat Stroke: Exposure to excessive heat can lead to a high fever, often accompanied by other symptoms like nausea, dizziness, and confusion.
• Blood Transfusions: Fever may occur as a reaction to a blood transfusion.
• Disorders of the Brain: Conditions affecting the brain, such as a brain tumor or encephalitis, can cause FUOs.
• Certain Cancers: Some types of cancer, including lymphoma and leukemia, can lead to unexplained fever.
• Autoimmune Diseases: Conditions where the body’s immune system mistakenly attacks its own tissues, such as lupus or rheumatoid arthritis, can sometimes cause FUOs.

Symptoms of Fever of Unknown Origin (FUOs)

The primary symptom of FUOs is a high fever, typically defined as a temperature of 100.4°F (38°C) or higher. Additional symptoms may include:

• Decreased activity or talkativeness
• Increased fussiness or irritability
• Decreased appetite and thirst
• Feeling warm or hot to the touch

It’s important to note that the measured temperature may not always reflect the perceived level of fever, as the body’s thermoregulatory mechanisms can be temporarily disrupted.

Fever Management in Children

In children, fever that is causing discomfort should be treated. However, it’s crucial to understand that treating the fever will not necessarily help the body get rid of the underlying infection any faster. Rather, the goal is to alleviate the child’s discomfort associated with the fever.

Some effective ways to manage fever in children include:

1. Administering antifever medications, such as acetaminophen or ibuprofen, to reduce the body temperature.
2. Dressing the child lightly to avoid trapping body heat.
3. Encouraging the child to drink plenty of fluids, such as water, juices, or popsicles.
4. Giving the child a lukewarm bath, being careful not to allow the child to shiver from cold water, as this can raise the body temperature.

It’s important to note that aspirin should not be given to children, as it has been linked to a serious, potentially fatal condition called Reye syndrome.

When to Seek Medical Attention

If a child experiences any of the following, it’s crucial to seek medical attention immediately:

• The child is 3 months old or younger and has a fever of 100.4°F (38°C) or higher.
• The child is of any age and has repeated fevers above 104°F (40°C).
• The child is younger than 2 years of age and has a fever of 100.4°F (38°C) that lasts for more than 1 day.
• The child is 2 years of age or older and has a fever of 100.4°F (38°C) that lasts for more than 3 days.
• The baby is fussy or crying and cannot be soothed.

In these cases, it’s essential to contact the child’s healthcare provider right away, as a high fever in a young infant can be a sign of a serious infection that requires prompt medical attention.

Specialized Care for Infectious Diseases

For children with complex or persistent infectious diseases, including FUOs, specialized care may be necessary. The Division of Infectious Diseases at Children’s National Hospital is a leading referral center for these conditions, providing comprehensive evaluation and treatment by a team of expert pediatric infectious disease specialists.

Conclusion

Fever of Unknown Origin (FUOs) is a condition where a high fever is not accompanied by any other obvious symptoms. Understanding the potential causes, managing the fever, and seeking timely medical attention when necessary are crucial for ensuring the well-being of individuals, especially children, experiencing this perplexing health issue.

Pediatric Fever of Unknown Origin – Conditions and Treatments

A fever is defined by most healthcare providers as a temperature of 100.4°F (38°C) and higher when taken rectally.

The body has several ways to maintain normal body temperature. The organs involved in helping with temperature regulation include the brain, skin, muscle and blood vessels. The body responds to changes in temperature by:

• Increasing or decreasing sweat production
• Moving blood away from, or closer to, the surface of the skin
• Getting rid of, or holding on to, water in the body
• Seeking a cooler or warmer environment

When your child has a fever, the body works the same way to control the temperature. But it has temporarily reset its thermostat at a higher temperature. The temperature increases for a number of reasons:

• Chemicals, called cytokines and mediators, are made in the body in response to an invasion from a microorganism, malignancy, or other intruder.
• The body is making more macrophages. These are cells that go to combat when intruders are present in the body. These cells actually “eat-up” the invading organism.
• The body is busy trying to make natural antibodies, which fight infection. These antibodies will recognize the infection next time it tries to invade.
• Many bacteria are enclosed in an overcoat-like membrane. When this membrane is disrupted or broken, the contents that escape can be toxic to the body. They stimulate the brain to raise the temperature.

• 
  

  These conditions can cause a fever:

  • Infectious diseases
  • Certain medicines
  • Heat stroke
  • Blood transfusion
  • Disorders in the brain
  • Some kinds of cancer
  • Some autoimmune diseases

• 
  

  Fever is not an illness. It is a symptom, or sign, that your body is fighting an illness or infection. Fever stimulates the body’s defenses, sending white blood cells and other “fighter” cells to fight and destroy the cause of the infection.

• 
  

  Children with fevers may become more uncomfortable as the temperature rises. Along with a body temperature greater than 100.4°F (38°C), symptoms may include:

  • Your child may not be as active or talkative as usual.
  • Your child may seem fussier, less hungry and thirstier.
  • Your child may feel warm or hot. Remember that even if your child feels like he or she is “burning up,” the measured temperature may not be that high.

  The symptoms of a fever may look like other health conditions. According to the American Academy of Pediatrics, if your child is younger than 3 months of age and has a temperature of 100.4°F (38°C) or higher, you should call your child’s healthcare provider right away. If you are unsure, always check with your child’s healthcare provider for a diagnosis.

• 
  

  In children, a fever that is making them uncomfortable should be treated. Treating your child’s fever will not help the body get rid of the infection any faster. It simply will relieve discomfort linked to the fever. Children between the ages of 6 months and 5 years can develop seizures from fever (called febrile seizures). If your child does have a febrile seizure, there is a chance that the seizure may occur again. But usually children outgrow the febrile seizures. A febrile seizure does not mean your child has epilepsy. There is no evidence that treating the fever will reduce the risk of having a febrile seizure.

• 
  

  Give your child an antifever medicine, such as acetaminophen or ibuprofen. DON’T give your child aspirin. It has been linked to a serious, potentially fatal disease, called Reye syndrome.

  Other ways to reduce a fever:

  • Dress your child lightly. Excess clothing will trap body heat and cause the temperature to rise.
  • Encourage your child to drink plenty of fluids, such as water, juices or popsicles.
  • Give your child a lukewarm bath. Do not allow your child to shiver from cold water. It can raise the body temperature. Never leave your child unattended in the bathtub.
  • Don’t use alcohol baths.

• 
  

  Unless advised otherwise by your child’s healthcare provider, call the provider right away if:

  • Your child is 3 months old or younger and has a fever of 100.4°F (38°C) or higher. Get medical care right away. Fever in a young baby can be a sign of a dangerous infection.
  • Your child is of any age and has repeated fevers above 104°F (40°C).
  • Your child is younger than 2 years of age and has a fever of 100.4°F (38°C) that lasts for more than 1 day.
  • Your child is age 2 or older and has a fever of 100.4°F (38°C) that lasts for more than 3 days.
  • Your baby is fussy or cries and can’t be soothed.

Infectious Diseases Treatment at Children’s National Hospital

Our Division of Infectious Diseases is the major referral center for infectious diseases in the Washington, D.C., area, helping thousands of young patients each year with contagious conditions. Discover more about the treatments we offer.

Learn about treatment

Help Kids and Make a Difference

Invest in future cures for some of life’s most devastating diseases. Give today to help more children grow up stronger.

Donate

Children’s Team Departments

Children’s Team

Children’s Team

Providers

Roberta DeBiasi

Division Chief, Infectious Diseases
Co-Director, Congenital Zika Program
Co-Director, Congenital Infection Program
Investigator, Children’s National Research Institute

Nada Harik

Director, Fellowship Training Program
Infectious Diseases Specialist

Alexandra Yonts

Director, Post COVID Program
Infectious Diseases Specialist

Departments

Departments

Infectious Diseases

Our Division of Infectious Diseases is the major referral center for infectious diseases in the Washington, D. C., area, helping thousands of patients each year, and actively promoting prevention through community outreach and education.

What Experts Say About Children with High Fever but No Symptoms

This article reviews what different experts say about children who have fevers but no other symptoms (yet). It pulls information from the American Academy of Pediatrics and several major children’s hospitals (see our sources below.)

The main takeaway: Fevers are a symptom of an underlying issue, often an infection. In toddlers or young children, they can start 24 hours before other symptoms kick in (like a runny nose or sore throat). That’s because they are one of the first ways the body starts fighting infection – one theory is that increased temperature makes it hard for infections to live in the body.

Read on where we will cover the possible causes of a fever, especially those without symptoms. We also discuss what a high fever is versus a mild fever (hint: it depends on the child’s age and thermometer/tool you are using…and there is a lot of variation among experts).

Disclaimer: This health information is for educational purposes only. Maternie articles are not written by medical professionals. You assume full responsibility for how you choose to use it. (And never hesitate to contact health care providers with questions!)

Causes of Fever (Without Other Symptoms)

Fever is not an illness itself, but a symptom of an illness. Most sources agree that fever is usually a sign of viral infections or bacterial infection, more often viral.

The American Academy of Pediatrics says a fever may be the only symptom your child experiences for the first 24 hours of a viral infection, before other symptoms, such as a runny nose or cough, appear.

Febrile Seizure Can Happen With No Other Symptoms

One scary thing that can happen with a fever but no other symptoms is febrile seizure. According to the National Institutes of Health, febrile seizures are most likely in children between the ages of six months and five years old, and are at the greatest risk of febrile seizure at age 2. They happen to approximately 2 to 5% of children age five and under in the United States.

They can occur with common child illnesses like a cold or the flu, and sometimes “a child may not have a fever at the time of the seizure but will develop one a few hours later.”

Febrile seizures are not caused by epilepsy, but can look very similar, as your child may lose consciousness and their arms and legs will shake uncontrollably. 

The NIH says to call an ambulance and go to the emergency department if a seizure lasts for more than five minutes. Thankfully, they write that febrile seizures under 15 minutes “do not cause any long-term health problems. Those that last more than 15 minutes are “generally harmless but do carry an increased risk of developing epilepsy.”

Tired of looking up what temperature is technically a fever?

Drop your email and we’ll send you a FREE, mobile-friendly graphic that breaks down what temps are technically a fever by your child’s age. Favorite it so you can access whenever!

Email(Required)

Other Causes: Roseola, UTIs, Sickle Cell Disease

The American Academy of Pediatrics also writes that Roseola is a “classic case” of unexplained fever in children between six months old and three years old. Typically a child would have a fever for 2 to 3 days, and then it will go away. A rash of small spots then appears on the chest and stomach, eventually spreading to the face. The rash disappears after 1 to 3 days and usually the child feels fine. 

Seattle Children’s Hospital says that a bladder infection, also known as urinary tract infections or a UTI, can be a common cause of fever in girls, especially if your child can’t express pain while urinating yet.

Lastly, children with Sickle Cell Disease (SCD) are more likely to get infections, according to Children’s National, especially bacterial infections. They write that fever “may be the first and only sign of infection.” Fevers can be deadly for children with SCD, and should be considered a medical emergency.

What Is a High Fever Versus Mild Fever in Children

There are a few important things to consider when identifying if your child actually has a fever, and then if it is high or mild. First is your child’s age. For infants younger than three months, any fever above 100.4° needs attention from a medical professional or potentially a trip to the emergency room. (Some sources had the cut off for this at two months, but the majority said three months or less.) One of the biggest concerns for young babies is an infection in the blood, which can become deadly quickly.

After that age, most experts viewed a fever as beginning around 100.4°F (some had the “fever” threshold temperature higher, like 101°F  from Norton’s Childrens’ or 102°F  from the UK’s National Health Service), but not requiring immediate attention unless the fever lasts for a day or more, or if it is accompanied by other symptoms. 

Children’s National Hospital had the following breakdown for parents to determine when a fever that needs medical attention includes…

• A child of any age with a high fever above 104°F 
• A child under two years with a fever of 100. 4°F that lasts for more than one day
• A child two years and older with a fever over 100.4 that lasts more than three days

Fever Threshold Can Also Depend on Thermometer Type

The type of thermometer you are using to take your child’s temperature can also affect temperature readings and how severe they are. Certain methods, like rectal, are more accurate than others, like under the arm measurements.

The American Academy of Pediatrics recommends using a digital thermometer (no old-fashioned mercury thermometers.) They also have the following thresholds for determining a high temperature that is a true fever:

• Ear, forehead, or rectal temperature: 100.4°F 
• Oral temperature: 100°F 
• Under the arm (armpit) temperature: 99°F

The best way to take their temperature will generally depend on their age. The AAP cautions that ear thermometers are not accurate in babies six months of age or younger. They also recommend not using oral thermometers until your child is four years or older. They have an illustrated guide on how to use a rectal thermometer here.

Keep in mind that your child’s normal body temperature can change throughout the day. The AAP provides this range:

• Normal rectal temperature: Anywhere from 96.8 F in the morning to a high of 100.3 F late in the day
• Normal oral temperature: Anywhere from 95.8 F in the morning to 99.9 F late in the day

Treating Your Child’s Fever at Home

Most sources agreed that the number one treatment for a fever at home is rest and making sure your child does not get dehydrated. You can use an oral rehydration solution, such as Pedialyte, or even ice pops to help ensure they are getting fluids. Signs of dehydration include not urinating frequently, so keep an eye on your child’s wet diapers or trips to the bathroom.

There was variation among sources on exactly when your child may need fever-reducing medication, like Tylenol or Advil. Seattle Children’s says medication is only needed if a fever is over 102 F. They also caution parents not to expect medication to reduce a fever by more than two or three degrees. Lastly, they write that sponging your child with cold water is “rarely needed” and could end up making your child more uncomfortable.

Sources:

Fever without Fear: Information for Parents – HealthyChildren.org

How to Take Your Child’s Temperature – HealthyChildren.org

Febrile Seizures Fact Sheet | National Institute of Neurological Disorders and Stroke (nih.gov)

When to Worry About a Child’s Fever | Sutter Health

Fever (seattlechildrens.org)

Unexplained Fever | Norton Children’s (nortonchildrens.com)

Fevers (for Parents) – Nemours KidsHealth

My Child Has a Fever: What Should I Do? | Children’s Hospital of Philadelphia (chop.edu)

Pediatric Fever of Unknown Origin – Conditions and Treatments | Children’s National Hospital (childrensnational.org)

Fever in children | NHS inform

What does the temperature indicate without other symptoms of the disease

April 1, 2022

Likbez

Health

Perhaps you are just too nervous.

What temperature is considered elevated

To begin with, let’s define the concepts. If you have 36.9 ° C and even 37 ° C, it is too early to talk about an elevated temperature. Normal body temperature is not necessarily 36.6 °C. It fluctuates over a fairly wide range.

The normal range is 36.1 to 37.2 °C.

If the thermometer shows values ​​above 37.2 °C, they speak of a fever. It is also elevated temperature, or simply temperature in the commonly used sense.

Most often this condition is caused by an infection. For example, viral – influenza or other common SARS. In this case, in addition to fever, you are likely to find other signs of a respiratory illness in yourself: sore throat, runny nose, headache.

However, it happens that there is a temperature, but there are no other symptoms – snot, nausea, rashes, lethargy, irritability. The reasons for this can be both harmless and deadly.

When to see a doctor immediately

A fever in itself is not a cause for alarm. But there are exceptions. Seek immediate medical attention if the temperature without symptoms:

• exceeds 38°C in an infant under three months of age or 38.9°C in a 3-6 month old child;
• has reached 38.9 °C and lasts longer than a day in a child under two years of age;
• arose after a child was left for a long time in a car standing under the sun;
• lasts longer than three days in a child;
• rose above 39.4 °C in an adult.

All this speaks of conditions that threaten health and even life.

If there are no danger signs, a fever without symptoms may be an indicator of some change in your lifestyle and may soon subside on its own. But it is not exactly.

What causes fever without other symptoms

Here are the most common factors that lead to fever.

1. Viral diseases

Most often, the symptoms of a cold or, for example, mononucleosis are obvious. But sometimes a viral infection can occur in a blurred form – without a pronounced cough, sore throat or runny nose. Nevertheless, even in this state, the body is actively fighting the infection, which is reported by an increase in temperature.

2. Bacterial infections

As with viruses, symptoms of bacterial infection are not always obvious. At least in the early stages of the disease. For example, tuberculosis may initially show nothing but weakness, which can easily be mistaken for the result of normal overwork, and a temperature of 37-37.5 ° C.

3. Taking certain medications

A mild but persistent fever may occur 7 to 10 days after you start taking a new drug. This condition is called drug fever.

Drug-induced fever without any other symptoms can be triggered by certain antibiotics (often from the penicillin or cephalosporin group), antihypertensive drugs, and anticonvulsants.

4. Autoimmune diseases

A mild fever is a common symptom of rheumatoid arthritis. It is believed that in this case, the fever is caused by an incipient inflammatory process in the joints. Another common disease that can make itself felt with fever without other symptoms is multiple sclerosis.

5. Some vaccinations

Diphtheria, tetanus, whooping cough, and pneumococcal vaccine can also raise fever.

6. Stress

Emotional state can affect body temperature. Doctors call this phenomenon psychogenic fever. Most often it occurs in overly impressionable young women, but can affect people regardless of gender and age. If we are talking about protracted experiences, chronic stress, the psychogenic temperature is kept within 37–38 °C. With high emotional stress, it can jump over 40 ° C.

7. Cancer

Some cancers, such as lymphomas and leukemia, sometimes cause persistent and unexplained fever.

8. Undetermined causes

Sometimes the cause of prolonged asymptomatic fever cannot be determined. In this case, the doctor will diagnose “fever of unknown origin.”

What to do with a temperature without other symptoms

Your task is to observe your condition and help the body cope with the internal disturbance that caused the temperature rise. For this:

• rest;
• drink plenty of fluids;
• observe the daily routine;
• walk, breathe fresh air;
• try to calm down and cope with stress, for example, stop watching the news for a while, listen to soothing music, practice measured deep breathing.

If the fever is caused by a mild viral illness or anxiety, it will go away by itself after 3-4 days.

But if the fever does not subside and even intensifies, acquires additional symptoms, you need to see a doctor. For starters, see a therapist. The doctor will ask you about how long the temperature lasts, ask questions about your well-being and lifestyle, conduct an examination and, most likely, offer to take blood and urine tests. The tests will help you find out if your body has inflammation or other disorders.

Depending on the results of the examination, the therapist will either give recommendations to help you cope with the temperature, or refer you to a specialized specialist – pulmonologist, gastroenterologist, rheumatologist, endocrinologist, oncologist – who will suggest further treatment options.

Read also 😷👩‍⚕️🤧

• How to quickly cure a runny nose
• 5 Flu Treatment Mistakes That Can Kill You
• SARS Treatment: Do’s and Don’ts
• 11 Symptoms of Pneumonia You Shouldn’t Miss0026
• The 14 most common and dangerous types of cancer

what disease and what to do

Fever is often one of the symptoms of the disease: cough, runny nose, diarrhea, nausea, or other signs that doctors or we we can diagnose the disease ourselves. But what does it mean if the temperature rises without symptoms?

Tags:

Coronavirus

Oncological diseases

infections

temperature

bacteria

Fever in children and adults

A temperature of 35.6 to 37.2 is considered normal, and most accept the “gold standard” of 36.6 as normal. Temperature fluctuations occur throughout the day and this is completely normal. To better understand the issue, also read why there is a low body temperature.

But when and why should you worry? An elevated temperature in adults is a temperature above 38 degrees that persists for some time. Most often, the temperature itself does not require special treatment, but it can cause severe weakness and discomfort – in this case, doctors recommend not to endure and accept it. Also, if there are no contraindications, you can try to bring down the temperature without medication.

In addition, the following signs should be cause for concern:

• temperature that does not fall and rises over time;
• breathing problems and chest pain;
• severe pain or swelling;

In this case, it is better to consult a doctor or call an ambulance.

Often, children have a slightly higher temperature than adults, and therefore they usually do not bring it down until the thermometer shows 38.5. However, it is important to monitor whether the temperature is rising and how quickly it happens – too high a temperature can provoke convulsions and other complications. You need to be especially careful if …

ADVERTISING – CONTINUED BELOW

• … the child has a fever without symptoms and it is difficult for him to eat and drink;
• …there is great weakness;
• …the temperature cannot be brought down, it rises again and again.

How do you know if the temperature is high?

Adults often understand that their temperature has risen, focusing on their own feelings. Additional signs – cold symptoms or symptoms of an intestinal infection will only confirm suspicions. However, if a high temperature has risen without symptoms, many believe that it just seems to them, because otherwise the state of health can be quite acceptable.

To be sure, of course, you should use a thermometer, but here are a few signs by which you can suspect a fever even without a thermometer.

Touch forehead

A method that most mothers are familiar with. They touch their forehead with their lips or the back of their hand. This approach works best if you need to detect the temperature in someone, and not in yourself. The person himself may not notice the rise in temperature in this way.

In other cases, deviations from the normal temperature will most likely be quite obvious, but, of course, this method cannot be called very accurate.

Pinch the skin on the arm

One of the signs that accompany high fever is dehydration. Fluid loss can be deadly for young children and should therefore not be tolerated. The simplest test for dehydration is to gently pinch the skin on your arm. If the crease is quickly smoothed out and the skin takes on its original appearance, then everything is ok. With dehydration, straightening will not occur instantly, but will take some time.

However, dehydration is far from being the only and not obligatory sign of fever.

Look at the face

An increase in temperature in children and adults is most often accompanied by reddening of the skin. On the face, especially on the cheeks, the color change will be especially noticeable. If you or your loved ones suddenly have reddened cheeks – and we are not talking about allergies – it may be a high temperature.

Pay attention to the color of the urine

Another sign associated with high fever and dehydration is a change in the color of the urine. Urine becomes more concentrated and darker in color, so orange or brown urine is also one of the common effects of fever.

Why you get a fever without symptoms: 5 possible causes

You can actually have a fever without obvious reasons. To describe this condition, a special term “fever of unknown origin” was coined, which is used in cases where the temperature rises above 38.3 degrees, but no other signs of the disease are observed. In order to establish the cause of fever without symptoms, you need to consult a doctor, take tests and undergo a series of examinations. Here are just some of the reasons that can cause fever in children and adults

Coronavirus infection

Coronavirus symptoms without fever include weakness, cough, trouble breathing, change or loss of smell, decreased appetite. But another situation is also possible: a fever without symptoms with covid will be the only sign indicating that something is going wrong in the body. Obvious signs of the disease may appear after a few days or not at all.

Common cold

Yes, colds caused by adenoviruses can often occur without typical cold symptoms – cough, runny nose, headache. A high temperature may be the only sign, and the rest, especially in adults, can often be minimally expressed – a person often does not notice other signs of illness, believing that he is simply tired or has not had enough sleep.

How to quickly bring down the temperature at home

Oncological diseases

Approximately one in three cases of fever of unknown origin is associated with cancer. Often, lymphoma and leukemia manifest in this way, which are difficult to identify without passing specific tests. Temperature without symptoms can also appear in other forms of cancer.