Infection stages – Understanding the progression of infectious diseases and their impact on health

In today’s world, where infectious diseases are a constant threat, it is crucial to understand the stages of infection in order to effectively diagnose and treat them. The journey from exposure to recovery can be categorized into four distinct stages, each with its own set of symptoms and outcomes.

The first stage is known as the incubation period. During this phase, the pathogen enters the body and starts to multiply. The length of the incubation period varies depending on the type of infection, ranging from a few hours to several months. Interestingly, this stage is characterized by the absence of any noticeable symptoms, making it challenging to identify the presence of the infection.

Next comes the prodromal stage, which is often referred to as the prelude to the acute phase. In this stage, the initial symptoms start to manifest, although they are usually non-specific and may resemble those of other illnesses. Patients may experience mild fever, fatigue, and general malaise. It is important to note that this is the stage when the pathogen is most contagious, increasing the risk of transmission to others.

The acute phase is when the infection reaches its peak, and the body’s immune system responds with full force. Symptoms are generally more severe and specific to the particular infection. Fever, cough, sore throat, body aches, and gastrointestinal issues are common in this stage. However, it is worth mentioning that the severity and duration of symptoms can vary from person to person, depending on various factors such as age, overall health, and the pathogen’s virulence.

The final stage of infection is the recovery stage. As the name suggests, this is when the body starts to heal, and symptoms gradually subside. The immune system successfully fights off the infection, and the patient’s overall condition improves. However, some infections have the potential to cause complications, leading to further health issues or even relapse. Additionally, certain infections can become chronic, persisting in the body for an extended period and requiring long-term management.

Understanding the four stages of infection is crucial in determining the appropriate course of action, from prevention and early detection to treatment and recovery. Recognizing the prodromal stage and its distinct symptoms can help in early intervention, reducing transmission rates and preventing complications. With this knowledge, healthcare professionals and individuals alike can work together to effectively combat infectious diseases and safeguard the well-being of the community.

Stage 1: Incubation Period and Initial Exposure

During stage 1 of an infection, known as the incubation period, the individual is exposed to the pathogen but may not experience any symptoms. This period can vary in length depending on the specific infectious agent and can range from a few hours to several weeks.

Initial exposure to the pathogen occurs through various means, such as contact with contaminated surfaces, airborne particles, or through direct contact with an infected individual. The individual may not be aware that they have been exposed during this time.

Prodromal Phase

Within the incubation period, the prodromal phase may occur. This phase is characterized by the onset of mild symptoms that are often non-specific and can be easily overlooked or attributed to other factors. Symptoms in the prodromal phase can include fatigue, headache, mild fever, and general malaise.

It is important to note that not all infections progress through a prodromal phase. Some infections may move directly from the incubation period to the acute phase, depending on the specific pathogen and the individual’s immune response.

Resolution and Recovery

After the incubation period and the potential prodromal phase, the infection may progress to the acute phase. During this stage, the individual experiences a more pronounced onset of symptoms, often specific to the type of infection. This is when the body’s immune system is actively fighting against the pathogen.

If the individual’s immune response is effective, the infection can resolve within a certain period of time. The body’s immune system successfully eliminates the pathogen, and the individual enters a recovery phase. During the recovery phase, symptoms gradually decrease and eventually disappear completely.

In some cases, complications can arise during the acute phase or later during the recovery phase. These complications can lead to the development of more severe symptoms or an extended duration of the infection. Certain infections can also become chronic, meaning they persist in the body for an extended period of time.

Understanding the four stages of infection, including the incubation period, initial exposure, prodromal phase, and subsequent resolution and recovery, can provide valuable insights into the progression and symptoms of different infectious diseases.

Stage 2: Invasion and Replication

After the incubation period, the infection enters the second stage known as invasion and replication. During this stage, the virus or bacteria has successfully penetrated the host’s body and starts to reproduce rapidly. This leads to a higher concentration of the pathogen in the body, resulting in the manifestation of symptoms.

The prodromal phase, which is part of the invasion and replication stage, is characterized by the onset of initial symptoms. These symptoms may be general and nonspecific, such as fatigue, fever, headache, and muscle aches. The prodromal phase serves as a warning sign that an infection is developing and prepares the immune system for the upcoming battle.

As the infection progresses, it enters the acute phase, where the symptoms become more severe and specific to the particular pathogen. The body’s immune system, with the help of various defense mechanisms, tries to combat the invading pathogen. However, at this stage, the battle is still ongoing, and the outcome is uncertain.

During the chronic phase, some infections can persist within the body for an extended period. This phase is characterized by milder symptoms or even the absence of symptoms altogether. However, the pathogen continues to replicate and slowly damages the body’s tissues. If left untreated, chronic infections can lead to long-term complications and sequelae.

In some cases, the resolution of the infection occurs naturally as the body’s immune system successfully eliminates the pathogen. This leads to recovery, where the symptoms gradually subside, and the individual returns to a normal, healthy state. However, in other cases, complications can arise, such as secondary infections or organ damage, which prolong the recovery process and may require additional medical interventions.

It is important to note that the progression of infection through these stages can vary depending on the specific pathogen, the individual’s immune response, and the availability of medical treatment. Understanding the different stages of infection can help in early detection, prompt treatment, and prevention of complications.

Stage 3: Prodromal Period

After the incubation period and the onset of symptoms, the infected individual enters the prodromal period, which is the third stage of infection. This period is characterized by the appearance of mild symptoms that signal the onset of the acute phase of the illness.

During the prodromal period, the symptoms gradually worsen and become more noticeable. The infected individual may experience a combination of general symptoms such as fatigue, malaise, and fever, as well as specific symptoms that are characteristic of the particular infection.

This stage is crucial as it often serves as an indication that the immune system is actively fighting the infection. However, it is important to note that not all infections have a clearly defined prodromal period. Some individuals may progress directly from the incubation period to the acute phase without experiencing any prodromal symptoms.

Progression and Complications

If left untreated or if the immune system is unable to effectively control the infection, the prodromal period can lead to further complications. The severity of these complications can vary depending on the type of infection and the individual’s overall health.

Some complications that may arise during the prodromal period include the development of secondary infections, organ damage, or the spread of the infection to other parts of the body. These complications can prolong the illness and increase the risk of severe illness or even death.

Recovery and Resolution

For most infections, the prodromal period marks the beginning of the acute phase, during which the symptoms peak in intensity. Following the acute phase, the body gradually recovers and enters the resolution stage, where the symptoms start to subside and the individual begins to feel better.

Recovery from the prodromal period and the subsequent acute phase can take time, and it is important to follow any prescribed treatments and rest as needed. In some cases, a relapse or the development of long-term sequelae, such as chronic fatigue or organ damage, may occur even after the resolution of the infection.

Overall, understanding the progression and symptoms of the prodromal period is crucial for effectively managing and treating infections. Recognizing the onset of this stage can help individuals seek appropriate medical care and take measures to prevent further complications.

Stage 4: Acute Phase and Full-blown Infection

Once the incubation period is over, the infected individual enters the acute phase of the infection. This is the stage where the symptoms become fully developed and the infection reaches its peak intensity.

The prodromal period, which is the initial phase of the acute stage, is characterized by the onset of symptoms such as fever, fatigue, headache, and muscle aches. During this phase, the infected individual may also experience a general feeling of malaise.

The acute phase of a full-blown infection typically lasts for a few days to a couple of weeks. The severity and duration of this stage can vary depending on the specific pathogen and the individual’s immune response.

Complications and Sequelae

In some cases, the acute phase of an infection can lead to complications. These complications may arise due to the direct effects of the pathogen on the body or the body’s immune response to the infection. Common complications can include pneumonia, organ failure, and secondary infections.

Once the acute phase is successfully managed, the infected individual enters the recovery phase. During this phase, the body gradually resolves the infection, and the symptoms start to improve. Depending on the severity of the infection, recovery can take anywhere from a few days to several weeks.

In certain cases, the infection may progress to a chronic phase. This occurs when the body is unable to completely eliminate the pathogen, and the infection persists over a long period of time. Chronic infections can lead to long-term health issues and may require ongoing medical treatment.

It is important to note that not all infections progress through all stages, and the progression and symptoms can vary depending on the specific pathogen and individual factors.

Stage 5: Common Symptoms

At this stage of infection, common symptoms may manifest, indicating the progression of the disease. These symptoms can vary depending on the specific pathogen and the individual’s immune response. It is important to note that not all individuals will experience the same symptoms, and some may exhibit more severe manifestations than others.

During the acute phase, individuals may experience symptoms such as fever, fatigue, body aches, and headache. These symptoms are often indicative of the body’s immune response to the infection and may last for several days.

Following the acute phase, individuals may enter the chronic stage of infection. During this phase, symptoms may persist for an extended period, sometimes lasting months or even years. Common chronic symptoms include persistent fatigue, joint pain, muscle weakness, and cognitive difficulties.

Some infections may also have sequelae, which are long-term consequences or complications resulting from the infection. These sequelae can range from mild to severe and may affect various organs or systems in the body. Examples of sequelae include organ damage, neurological disorders, and impaired immune function.

Relapse is another possible outcome, especially in infections caused by certain pathogens. After a period of apparent resolution, symptoms may reappear, indicating a relapse of the infection. This can be due to various factors, such as incomplete eradication of the pathogen or reactivation of dormant infections.

It is important to note that during the incubation period, individuals may not exhibit any symptoms. This period refers to the time between initial exposure to the pathogen and the onset of symptoms. The duration of the incubation period can vary depending on the specific infection and may range from a few days to several weeks.

Recovery from an infection can vary depending on various factors, including the individual’s immune response and the specific pathogen. Some individuals may recover completely without any long-term complications. Others may experience a prolonged recovery period or persistent symptoms even after the infection has resolved.

Stage	Common Symptoms
Acute	Fever, fatigue, body aches, headache
Chronic	Persistent fatigue, joint pain, muscle weakness, cognitive difficulties
Sequelae	Organ damage, neurological disorders, impaired immune function
Relapse	Reappearance of symptoms after apparent resolution
Incubation	No symptoms, time between exposure and symptom onset
Recovery	Varies depending on individual and pathogen
Resolution	Complete resolution of symptoms, return to normal health

Stage 6: Respiratory Symptoms

During the respiratory symptoms stage of infection, the virus has reached the respiratory system and begins to affect the lungs and airways. This stage typically follows the resolution of the prodromal stage, where general symptoms such as fever and fatigue start to subside.

Respiratory symptoms can vary in severity depending on the individual and the specific virus causing the infection. Common symptoms include coughing, shortness of breath, chest pain or discomfort, and wheezing. These symptoms are often indicative of inflammation and congestion in the respiratory system.

In some cases, respiratory symptoms can lead to complications such as pneumonia, bronchitis, or respiratory failure. These complications may require additional medical intervention and can prolong the overall recovery process. It is important to seek medical attention if respiratory symptoms worsen or do not improve over time.

Once the respiratory symptoms begin to improve, the individual is considered to be in the recovery stage. During this stage, the body continues to fight off the infection, and the immune system works to clear the virus from the respiratory system. The length of the recovery stage can vary depending on the individual and the severity of the infection.

In rare cases, some individuals may experience sequelae or long-term effects related to the respiratory symptoms. These could include chronic lung damage, decreased lung function, or respiratory conditions that persist even after the infection is resolved. Similarly, some individuals may experience relapses of respiratory symptoms, where the symptoms reoccur after a period of improvement.

To aid in recovery and prevent complications, it is important to rest, stay hydrated, and follow any prescribed treatments or medications. A healthy lifestyle, including a balanced diet and regular exercise, can also support the immune system and promote overall respiratory health.

Stage 7: Gastrointestinal Symptoms

During the seventh stage of infection, known as the gastrointestinal stage, individuals may experience a range of symptoms related to the digestive system. These symptoms can vary in severity and duration, and may include:

Symptom	Description
Nausea	A feeling of queasiness or unease in the stomach, often accompanied by a desire to vomit.
Vomiting	The forceful expulsion of stomach contents through the mouth.
Diarrhea	Loose, watery stools that occur more frequently than usual.
Abdominal pain	Discomfort or cramping in the stomach or belly area.
Loss of appetite	A reduced desire to eat or lack of interest in food.
Dehydration	A condition that occurs when the body loses more fluid than it takes in, leading to an imbalance.

These gastrointestinal symptoms can be a result of the infection spreading to the intestines or the body’s immune response to the infection. In some cases, these symptoms may resolve on their own with time and rest. However, complications such as dehydration may arise, requiring medical intervention.

It is important for individuals in this stage to manage their symptoms and seek appropriate medical care if necessary. Depending on the severity of the symptoms, healthcare professionals may recommend rest, hydration, and specific dietary changes. In some cases, medications may be prescribed to alleviate symptoms or treat complications.

It is also important to note that while some individuals may experience a complete resolution of symptoms after this stage, others may go on to experience additional stages, such as relapse or the development of sequelae. The duration of this stage can vary depending on the individual and the specific infection.

Stage 8: Neurological Symptoms

Neurological symptoms can occur during the acute phase of infection, as well as during the recovery, relapse, and complication stages. These symptoms can be a result of direct viral invasion or secondary effects of the virus on the nervous system.

During the acute stage of infection, some individuals may experience neurological symptoms such as headache, dizziness, and confusion. These symptoms are often mild and transient, resolving within a few days or weeks.

In some cases, however, neurological symptoms can persist during the recovery stage. These symptoms may include persistent headaches, difficulty concentrating, and memory problems.

During the relapse stage, neurological symptoms can reappear or worsen. This can be a result of the virus reactivating or causing further damage to the nervous system.

Complications can also arise during this stage, leading to more serious neurological symptoms. These complications can include encephalitis, meningitis, and stroke.

With proper medical attention and treatment, most individuals can recover from these neurological symptoms. However, some individuals may experience long-term neurological sequelae, such as cognitive impairments or motor dysfunction.

It is important to note that neurological symptoms can also occur during the incubation period of the infection. This is the stage between exposure to the virus and the onset of symptoms. Neurological symptoms during this stage are rare, but can include loss of smell or taste.

In chronic cases of infection, neurological symptoms can persist for an extended period of time. These symptoms may be intermittent and can vary in severity.

If you experience any neurological symptoms during any stage of infection, it is important to seek medical attention for proper diagnosis and treatment.

Stage 9: Cutaneous Symptoms

During the acute stage of infection, it is common for individuals to experience cutaneous symptoms. Cutaneous symptoms refer to any symptoms that affect the skin. These symptoms can range from mild to severe and can manifest in various ways, depending on the type of infection.

In the incubation period, individuals may not experience any cutaneous symptoms. However, as the infection progresses to the chronic stage, cutaneous symptoms may start to appear. These symptoms can include rashes, blisters, lesions, or discoloration of the skin. The severity of these symptoms can vary from person to person, with some individuals experiencing only mild symptoms while others may have severe symptoms that affect their daily activities.

In some cases, cutaneous symptoms can lead to complications. Complications can occur when the infection spreads to other parts of the body or when the immune system reacts strongly to the infection. These complications can result in more severe cutaneous symptoms or can even lead to other health issues.

After the acute stage of infection, individuals may experience sequelae or long-term effects of the infection. These sequelae can include persistent cutaneous symptoms, such as scarring or changes in pigmentation. These long-term effects can vary from person to person and can depend on factors such as the severity of the infection and the individual’s immune response.

In some cases, individuals may experience a relapse of cutaneous symptoms even after the resolution of the infection. This can occur if the infection was not completely cleared from the body or if the immune system is compromised. It is important for individuals to seek medical attention if they experience a relapse of cutaneous symptoms, as it may indicate a recurrence of the infection or another underlying health issue.

In conclusion, cutaneous symptoms can occur at various stages of infection, from the acute stage to the chronic stage and even after the resolution of the infection. These symptoms can range from mild to severe and can have long-term effects on the skin. It is important for individuals to be aware of these symptoms and seek medical attention if necessary to ensure proper diagnosis and treatment.

Stage 10: Hematological Symptoms

Hematological symptoms are commonly seen during the recovery phase of an infection. This stage comes after the acute phase, which is characterized by the onset of symptoms and the development of complications.

During this stage, the body’s hematological system starts to stabilize and return to normal. The prodromal symptoms, which are general symptoms that occur before the onset of the infection, begin to resolve. The body starts to produce more white blood cells, which are responsible for fighting off infection.

In some cases, there may be a relapse of hematological symptoms. This can occur if the infection is not completely resolved during the acute phase. The relapse can be caused by a reactivation of the virus or a new strain of bacteria.

Common Hematological Symptoms:

• Fatigue
• Anemia
• Leukopenia (low white blood cell count)
• Thrombocytopenia (low platelet count)

Hematological symptoms can also be seen during the incubation period, which is the time between when a person is exposed to the infection and when symptoms first appear. However, the symptoms are usually mild during this stage and may not be noticeable.

If hematological symptoms persist or worsen during the resolution phase, it may indicate a complication or progression to a chronic infection. In such cases, additional medical intervention may be necessary.

It is important to monitor hematological symptoms closely during the different stages of infection to ensure proper diagnosis and treatment. Regular blood tests may be done to track the changes in the hematological system and guide the treatment plan.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a healthcare professional for proper diagnosis and treatment of any infection.

Stage 11: Musculoskeletal Symptoms

During the musculoskeletal symptom stage of infection, individuals may experience acute pain, stiffness, and swelling in their muscles, joints, and bones. These symptoms often occur after the prodromal stage and can be a result of the body’s immune response to the infection.

The musculoskeletal symptoms can vary in intensity and duration, depending on the individual and the specific pathogen causing the infection. Some individuals may only experience mild discomfort, while others may have severe pain and limited mobility.

In some cases, musculoskeletal symptoms may be a sequelae of the infection, meaning they can persist even after the infection has resolved. This is more commonly seen in certain viral infections, such as Zika virus or Chikungunya virus.

Recovery from musculoskeletal symptoms typically involves rest, pain management, and physical therapy to improve strength and mobility. In cases where the symptoms are severe or persistent, more intensive treatment may be necessary.

It is important to note that musculoskeletal symptoms can also be a complication of the infection and may require additional medical intervention. Complications can include inflammation of the joints, damage to the bones or cartilage, or infections of the surrounding tissue.

In rare cases, individuals may experience a relapse of musculoskeletal symptoms after a period of resolution or recovery. This can be due to the reactivation of the virus or bacteria causing the initial infection or a reinfection with the same pathogen.

Overall, musculoskeletal symptoms during the infection’s progression can greatly impact an individual’s quality of life. It is important to seek medical attention if you experience any of these symptoms to receive an accurate diagnosis and appropriate treatment.

Stage 12: Genitourinary Symptoms

Genitourinary symptoms can occur as part of the progression of some infectious diseases. These symptoms may indicate that the infection has reached the genitourinary tract, which includes the organs of the reproductive and urinary systems. It is important to note that not all infections progress to this stage, and the presence of genitourinary symptoms does not always indicate a severe or advanced infection.

The genitourinary stage typically occurs after the initial stages of infection, such as the acute and prodromal stages. During this stage, the virus or bacteria may have already passed through the bloodstream or other body systems, reaching the genitourinary tract.

Patients experiencing genitourinary symptoms may notice changes in the urinary system, such as increased frequency or urgency of urination, painful urination, cloudy or bloody urine, or difficulty emptying the bladder completely. Infections that affect the reproductive system can also cause symptoms such as vaginal discharge, abnormal bleeding, pelvic pain, or testicular pain in males.

In some cases, genitourinary symptoms may be accompanied by complications. These complications can include kidney infections, urinary tract infections, pelvic inflammatory disease, or sexually transmitted infections. It is important to seek medical attention if you experience these symptoms or suspect an infection.

The genitourinary stage can vary in duration depending on the specific infection and individual factors. In some cases, the symptoms may resolve on their own with proper rest, hydration, and symptomatic treatment. However, if the infection is not properly treated or if there are underlying health conditions, the infection may progress to a chronic stage or lead to relapse.

It is important to note that some infections can have long-term effects or sequelae on the genitourinary system. These sequelae can include infertility, chronic pain, scarring, or other complications that may require ongoing medical management.

Common Genitourinary Symptoms
Increased frequency or urgency of urination	Vaginal discharge
Painful urination	Abnormal bleeding
Cloudy or bloody urine	Pelvic pain
Difficulty emptying the bladder completely	Testicular pain in males

Stage 13: Psychological Symptoms

During the progression of an infection, there are various stages that an individual may experience. These stages can include the incubation period, relapse, complication, resolution, and even chronic and acute sequelae. However, one stage that is often overlooked is the stage of psychological symptoms.

Psychological symptoms can occur during any stage of an infection and can range from mild to severe. These symptoms often manifest as changes in mood, behavior, and cognition. Common psychological symptoms include anxiety, depression, irritability, confusion, and difficulty concentrating.

The presence of psychological symptoms can have a significant impact on an individual’s overall well-being and quality of life. These symptoms can affect a person’s ability to perform daily activities, maintain relationships, and even work or attend school. It is important to recognize and address these symptoms in order to provide appropriate support and treatment.

Psychological Symptoms	Description
Anxiety	A feeling of unease, such as excessive worry or fear
Depression	A persistent feeling of sadness or loss of interest
Irritability	A heightened sensitivity and tendency to become easily annoyed
Confusion	Disorientation or difficulty thinking clearly
Difficulty concentrating	A decreased ability to focus or pay attention

It is important to note that these psychological symptoms can also be present during the prodromal stage of an infection, which is the stage immediately preceding the onset of physical symptoms. Therefore, early recognition and intervention are crucial in order to prevent the progression of these symptoms and mitigate their impact on an individual’s mental health.

Stage 14: Complications and Risk Factors

Complications can occur at any stage of infection, but they are most common in the acute and chronic phases. Acute complications may arise during the prodromal period or shortly after the infection has been established. They can range from mild to severe and may include symptoms such as fever, headache, muscle aches, and fatigue.

Some acute complications can lead to more serious conditions, known as sequelae. These can include pneumonia, encephalitis, and other organ and tissue damage. In some cases, the infection may relapse or become chronic, leading to long-term complications and symptoms.

Risk factors for complications vary depending on the specific infection. Certain individuals may be more prone to developing severe symptoms or complications due to factors such as age, underlying health conditions, or a weakened immune system. However, even healthy individuals can experience complications if the infection is severe or if they are exposed to certain risk factors.

Early recognition and treatment of complications are vital for preventing further health problems. If you experience any worsening or new symptoms during the course of an infection, it is important to seek medical attention. Your healthcare provider can evaluate your condition and provide appropriate treatment to help resolve any complications and reduce the risk of long-term effects.

Stage 15: Recovery and Post-Infection Period

After the acute phase of the infection, the body enters the stage of recovery. During this stage, the immune system continues to fight off any remaining pathogens and the symptoms begin to subside.

Resolution of symptoms may vary depending on the individual’s overall health and the specific infection. In some cases, the recovery period may be relatively mild and short-lived. However, in other cases, particularly for severe or chronic infections, the recovery process may take longer and be more challenging.

The post-infection period, also referred to as the convalescent period, is the time when the body fully recovers from the infection. During this time, the individual may still experience fatigue and general weakness as the body regains its strength. It is important to allow sufficient time for rest and recovery during this period to ensure a complete and healthy recovery.

While most individuals fully recover from infections without any long-term sequelae, some infections may leave lasting effects on the body. These sequelae, such as organ damage or neurological complications, may require additional medical care and monitoring even after the infection has resolved.

It is important to note that recovery from an infection does not guarantee immunity against future infections. In some cases, individuals may experience relapses or become susceptible to reinfection. Therefore, it is crucial to continue practicing good hygiene and taking appropriate preventive measures even after recovering from an infection.

The duration of the recovery and post-infection period can vary depending on the specific infection, the individual’s immune response, and other factors. It is important to consult with a healthcare provider for guidance on the appropriate steps to take during this stage and to monitor for any potential complications.

Question and answer:

What are the four stages of infection?

The four stages of infection are incubation, prodromal, acute illness, and convalescence.

What happens during the incubation period?

During the incubation period, the infectious agent begins to multiply in the body, but the person does not yet show any symptoms of illness.

What are the symptoms of the prodromal stage?

The prodromal stage is characterized by the onset of mild symptoms, such as fatigue, headache, and a general feeling of malaise.

What is the duration of the acute illness stage?

The acute illness stage typically lasts for a few days to a couple of weeks, during which the person experiences the full onset of symptoms associated with the infection.

How long does the convalescence stage last?

The convalescence stage is the period of recovery, during which the person gradually regains their strength and returns to their normal state of health. The length of this stage can vary depending on the individual and the severity of the infection.

What are the four stages of infection?

The four stages of infection are incubation, prodromal, acute, and convalescent.

How long does the incubation stage typically last?

The incubation stage can last from a few hours to several months, depending on the type of infection.

What are the common symptoms during the prodromal stage of infection?

Common symptoms during the prodromal stage include fatigue, headache, fever, and general malaise.