Fever
Fever can mean a cold, flu, or something more. Fast on-site testing and same-day treatment available.
目次
When you have a fever, the cause is not always just "the common cold," "influenza," or "COVID-19." It could also be a bacterial infection, urinary tract infection, pneumonia, or other conditions requiring appropriate treatment. At our clinic, we identify the cause of your fever and provide examinations and treatments tailored to your symptoms.
- Rapid tests available for influenza, COVID-19, and strep throat
- Diagnosing the cause of fever through examination and tests
- Treatment tailored to symptoms, including antipyretics, antibiotics, and IV fluids
- Walk-ins and same-day appointments are welcome
ABOUT
What is a fever?
Normal body temperature is usually around 36-37℃ (96.8-98.6°F). Generally, 37.5℃ (99.5°F) or higher is considered a "fever," and 38.0℃ (100.4°F) or higher is a "high fever." Fever is a sign that your body is fighting off pathogens, which is a normal function of the immune system. However, if symptoms persist for a long time or if there is a risk of complications, it is important to seek medical attention early.
Body temperature guidelines
| Temperature | Category/Action |
|---|---|
| 〜37.4℃ (〜99.3°F) | Normal to low-grade fever. Often observed with watchful waiting. |
| 37.5〜37.9℃ (99.5〜100.2°F) | Low-grade fever to fever. Consider seeing a doctor if symptoms persist. |
| 38.0〜38.9℃ (100.4〜102.0°F) | Fever. High probability of infection, early medical attention recommended. |
| 39.0℃ (102.2°F) or higher | High fever. Strong recommendation for immediate medical attention. |
Warning signs requiring early medical attention
- High fever of 38.5℃ (101.3°F) or higher that lasts for 2-3 days or more
- Fever that does not go down even with antipyretics
- Severe headache, neck pain, sensitivity to light
- Difficulty breathing, chest pain, decreased SpO₂
- Pain during urination, lower back pain
- Fever in elderly individuals, infants, pregnant women, or those with weakened immune systems
- Fever after international travel
CAUSES
Main causes of fever
The causes of fever are diverse, but they are broadly classified into "viral infections," "bacterial infections," and "other diseases." We will explain the seven most common causes.
Common cold syndrome
The most common cause of fever. An upper respiratory infection caused by over 200 types of viruses, usually resolving naturally within a week.
Main symptoms
- Runny nose/nasal congestion
- Sore throat/discomfort
- Sneezing/coughing
- Low-grade fever up to around 38℃ (100.4°F)
- Mild fatigue/headache
Tests/Treatment
- Antibiotics are not needed as the cause is viral
- Symptomatic treatment (antipyretics, cough medicine, nasal decongestants, etc.) is the basic approach
💡 Unnecessary use of antibiotics can lead to the emergence of antibiotic-resistant bacteria.
Influenza
Characterized by a sudden high fever of 38-40℃ (100.4-104°F) and severe general malaise. It is a highly contagious infection that spreads every autumn and winter.
Main symptoms
- Sudden high fever (38-40℃ (100.4-104°F) or higher)
- Severe general malaise, muscle pain, joint pain
- Headache, chills, loss of appetite
- Sore throat, cough, runny nose
- Febrile seizures in children, rarely encephalopathy
Tests/Treatment
- Rapid antigen testing is best performed 12-48 hours after onset
- Antiviral drugs (Tamiflu, Inavir, Xofluza, etc.) are effective within 48 hours of onset
💡 Annual vaccination between October and November can reduce the risk of severe illness, hospitalization, and death.
Comparison of Common Cold and Influenza
| Item | Common Cold | Influenza |
|---|---|---|
| Onset | Gradual | Sudden (rapid within hours) |
| Fever | Low-grade fever to 38℃ (100.4°F) | High fever of 38-40℃ (100.4-104°F) |
| Systemic symptoms | Relatively mild | Severe malaise, muscle pain |
| Nasal/throat symptoms | Primary symptoms | Milder than systemic symptoms |
| Medication | Symptomatic treatment only | Antiviral drugs are effective |
COVID-19 (Coronavirus Disease 2019)
As of May 2023, it is classified as a Class 5 infectious disease. Symptoms range widely from asymptomatic to severe, with the elderly and those with underlying medical conditions at higher risk of severe illness.
Main symptoms
- Fever, chills, fatigue
- Sore throat, runny nose, cough
- Headache, muscle pain, joint pain
- Loss of smell and taste (characteristic)
- Difficulty breathing, pneumonia (in severe cases)
Tests/Treatment
- Rapid antigen tests are highly sensitive up to day 3 after onset
- Antiviral drugs (Paxlovid, Lagevrio) are effective in preventing severe illness if taken within 5 days of onset
- Our clinic also offers simultaneous testing for COVID-19 and influenza
Streptococcal infection/Tonsillitis
An infection caused by Group A Streptococcus. While common in children, adults can also be infected, and stopping treatment prematurely carries a risk of serious complications such as rheumatic fever and nephritis.
Main symptoms
- Sudden high fever (38-40℃ (100.4-104°F))
- Severe sore throat, redness, white pus
- Swollen lymph nodes in the neck and jaw area
- Strawberry tongue, red rash on the trunk (scarlet fever)
- Notably, runny nose and cough are uncommon
Tests/Treatment
- Rapid antigen test provides results in approximately 5-10 minutes
- Penicillin-based antibiotics (amoxicillin) are usually taken for 10 days
💡 Even if symptoms improve, continue taking antibiotics until the entire course is finished. Stopping prematurely can leave bacteria behind and increase the risk of complications.
Urinary tract infection (Cystitis/Pyelonephritis)
An infection caused by bacteria such as E. coli. Women are more susceptible due to their shorter urethra, and if fever is present, it may indicate pyelonephritis.
Main symptoms
- Cystitis: Pain during urination, frequent urination, feeling of incomplete bladder emptying, cloudy urine (fever is mild)
- Pyelonephritis: High fever of 38-39℃ (100.4-102.2°F) or higher, chills and shivering, tenderness in the flank/lower back, nausea
Tests/Treatment
- Urine test to check for white blood cells, bacteria, and nitrites
- If necessary, urine culture to identify the causative bacteria
- Cystitis: 3-7 days of oral antibiotics; Pyelonephritis: approximately 2 weeks of oral antibiotics
- Severe cases may require intravenous fluids and hospitalization
💡 "Fever + back pain" suggests pyelonephritis. Leaving it untreated can lead to a risk of sepsis.
Pneumonia
An infection that causes inflammation in the alveoli. The causes are diverse, including viruses, bacteria, and fungi, and elderly individuals may only experience atypical symptoms.
Main symptoms
- High fever of 38-39℃ (100.4-102.2°F) or higher, chills
- Shortness of breath, difficulty breathing
- Wet cough, yellow to green sputum
- Chest pain (when breathing deeply)
- Mycoplasma pneumonia may cause a dry cough lasting 2-3 weeks
Tests/Treatment
- Diagnosis through auscultation, chest X-ray, blood tests, and SpO₂ measurement
- Mild cases are treated with oral antibiotics on an outpatient basis
- Severe cases require hospitalization
💡 If SpO₂ is below 93% or lips are purple, seek emergency medical attention immediately.
Other causes of fever
For recurrent fevers, low-grade fevers lasting several weeks, or fevers of unknown origin, we differentiate between the following conditions:
Main conditions
- Autoimmune diseases (SLE, rheumatoid arthritis, etc.)
- Malignancies (cancer, lymphoma)
- Drug-induced fever
- Heatstroke, thyroid storm
- Imported infections (malaria, dengue fever, etc.)
💡 A "fever of unknown origin" (FUO) of 38℃ (100.4°F) or higher lasting for more than 3 weeks requires specialized investigation.
HOME CARE
Home care
When you have a fever, do not push yourself and prioritize your body's recovery. Keep the following four points in mind:
Hydration
Drink water, sports drinks, or oral rehydration solutions (such as OS-1) frequently in small sips. If your urine is dark yellow to brown, it is a sign of dehydration.
Rest and sleep
Rest is essential for your body to fight infection. Overexertion can delay recovery and increase the risk of spreading the infection to others.
How to use antipyretics
Use when your temperature is 38.5℃ (101.3°F) or higher and you feel unwell. The purpose is not just to "lower the fever," but to reduce strain on the body and promote rest.
Do not use aspirin (Bufferin) for children under 15 years old (risk of Reye's syndrome).
Diet
Loss of appetite is natural. Do not force yourself to eat; instead, eat small amounts of easily digestible foods (such as rice porridge, udon noodles, or soup). Avoid greasy foods, irritants, and alcohol.
When to stop home care and seek medical attention
- Fever does not go down even with antipyretics
- Fever of 39℃ (102.2°F) or higher lasts for more than 3 days
- Unable to consume any fluids
- Difficulty breathing / feeling lightheaded or disoriented
- Numbness or paralysis in any part of the body
- Rash spreading rapidly
EXAMINATION
Examinations and treatment at our clinic
To accurately determine the cause of your fever, we conduct the following tests depending on your symptoms:
| Test/Procedure | Purpose/What it reveals |
|---|---|
| Influenza rapid test | Confirms Type A and B in about 15 minutes |
| COVID-19/Influenza co-test | Detects both with a single test |
| Strep throat rapid test | Confirms streptococcal infection in the throat in about 10 minutes |
| Blood test | White blood cell count, CRP, liver/kidney function, differentiation between bacterial/viral |
| Urinalysis | Confirms urinary tract infection |
| Chest X-ray | Confirms presence of pneumonia/pleural effusion |
| SpO₂ measurement | Measures blood oxygen saturation, assesses severity of respiratory disease |
| Intravenous fluids (IV) | Corrects dehydration, replenishes fluids and electrolytes |
Our clinic's treatment policy
Based on test results, we will carefully explain "why you have a fever." Antibiotics will only be prescribed if necessary, based on the diagnosis.
FLOW
Visit flow
A visit for fever proceeds in the following 6 steps:
WEB reservation or direct visit
To prevent infection, please contact us by phone or WEB reservation before visiting. Please cooperate by wearing a mask.
Reception and filling out medical questionnaire
You will fill out information regarding the onset of fever, temperature changes, other symptoms, history of overseas travel, and local infection status.
Doctor's consultation
We will measure your temperature, blood pressure, and SpO₂, perform a visual inspection of your throat, auscultation, and abdominal palpation, and propose necessary tests.
Various tests
Depending on your symptoms, we will conduct rapid tests (influenza, COVID-19, strep throat), blood tests, urinalysis, chest X-rays, etc.
Explanation of results, prescription, and IV fluids
We will explain the diagnosis based on the test results and prescribe medication or administer IV fluids.
Payment and return home
We will explain precautions for your life after returning home and provide contact information in case your symptoms worsen the next day or later.
FAQ
Frequently Asked Questions
Should I go to the hospital immediately if I have a fever?
If you are an adult with a temperature below 38℃ (100.4°F) and other symptoms are mild, you can monitor your condition at home while staying hydrated and resting. However, if your temperature is 38.5℃ (101.3°F) or higher for 2-3 days, you have difficulty breathing, cannot consume fluids, are elderly, an infant, pregnant, or have a fever after international travel, we recommend seeking medical attention early.
Do antibiotics work for the common cold?
Since the common cold is caused by viruses, antibiotics are ineffective. Unnecessary use can lead to the emergence of antibiotic-resistant bacteria, so we only prescribe them when necessary based on diagnosis.
Is the influenza test accurate immediately after onset?
The accuracy is highest 12-24 hours after onset. Immediately after onset (within 6 hours), the viral load may be low, leading to a false negative. Therefore, if symptoms are severe despite a negative result, we recommend retesting the next day or later.
Can I go to work or school after my fever has gone down?
For influenza, it is recommended to refrain from going out until 48 hours have passed since the fever subsided. For COVID-19, it is recommended to refrain from going out until 5 days have passed since onset and 24 hours have passed since symptoms improved.
Does taking antipyretics delay recovery?
Fever is part of the immune response, so theoretically, some delay might occur. However, in reality, physical exhaustion from high fever and difficulty consuming fluids hinder recovery more. Antipyretics are used to "reduce the burden on the body and promote rest and hydration."
I've had a low-grade fever for several weeks. Should I see a doctor?
If you have a low-grade fever of around 37-37.5℃ (98.6-99.5°F) that lasts for 2-3 weeks or more, we recommend seeing a doctor. It could be an indicator of underlying conditions that should not be ignored, such as chronic infections like tuberculosis, autoimmune diseases, thyroid disorders, or malignancies.
My child has a fever, should I go to a pediatrician?
Our clinic is an internal medicine clinic that primarily treats individuals 15 years and older. For children with a fever, we recommend visiting their regular pediatrician.
Does getting an IV help fever go down faster?
Intravenous fluids (IV) help correct dehydration and aid in your body's recovery. While it is possible to mix antipyretics into the IV to lower fever, the IV itself does not cure the infection.
Summary
The causes of fever are diverse, and self-diagnosing and leaving it untreated can sometimes lead to severe complications. If you have any concerning symptoms, please feel free to consult our clinic.
- Rapid tests for influenza, COVID-19, and strep throat provide results in 10-15 minutes
- Seek early medical attention for fever + back pain or fever + difficulty breathing
- Antibiotics should only be taken when necessary, and the full course should be completed
- Walk-ins and same-day appointments are welcome
