Complement component 3 deficiency is a rare genetic condition that affects the immune system. People with complement component 3 deficiency often have repeated bacterial infections and sometimes severe infections of the lungs, ears, skin, or blood. It usually starts in infancy or childhood and tends to be lifelong. Treatment focuses on prompt antibiotics, regular vaccines, and sometimes preventive antibiotics, and outcomes vary with how quickly infections are treated. Not everyone will have the same experience, and regular follow-up with an immunology team can lower the risk of serious illness.
Overview
Complement component 3 deficiencySymptoms
Complement component 3 deficiency often appears in infancy or early childhood with frequent, serious bacterial infections—pneumonia, ear or sinus infections, bloodstream infections, or meningitis. People may heal slowly. Some develop autoimmune features, such as rashes or kidney problems.
Outlook and prognosis
Many living with Complement component 3 deficiency face repeated bacterial infections early in life, especially of the ears, lungs, blood, and brain coverings. With prompt antibiotics, vaccines, and specialist follow-up, most infections can be prevented or treated quickly. Long-term outlook improves with an action plan for fevers and regular monitoring for autoimmune features.
Causes and risk factors
Complement component 3 deficiency usually results from inheriting two altered C3 genes (autosomal recessive). Risk rises with family history or parental relatedness; some ancestries have higher rates. Infection exposure and incomplete vaccination modify severity, not cause.
Genetic influences
Genetics are central in Complement component 3 deficiency. Most cases arise from inherited C3 gene variants that reduce or disrupt C3 protein, raising infection risk. Family history matters; carriers may be healthy but can pass variants to children.
Diagnosis
Doctors assess history of recurrent severe bacterial infections, low C3 levels and absent hemolytic complement activity. Confirmation uses complement pathway assays and genetic tests of the C3 gene. Early genetic diagnosis of Complement component 3 deficiency supports counseling for families.
Treatment and drugs
Treatment for complement component 3 deficiency focuses on preventing and promptly treating infections. Care often includes up‑to‑date vaccines (including meningococcal and pneumococcal), prophylactic antibiotics in some cases, and rapid antibiotics for any fever. Some may benefit from immunology follow‑up, infection‑prevention plans, and genetic counseling.
Symptoms
People with complement component 3 deficiency often face frequent or unusually severe bacterial infections, especially in the ears, sinuses, lungs, or the lining around the brain and spinal cord. Early features of complement component 3 deficiency often include repeated infections that are hard to shake and tend to come back. Some also develop autoimmune issues, like joint pain, rashes, or kidney inflammation. Features vary from person to person and can change over time.
Frequent bacterial infections that return over short intervals. They often start in early childhood and may be more severe than expected for routine bugs. People with complement component 3 deficiency may need antibiotics more often.
Ear pain, drainage, or temporary hearing trouble and sinus pressure are common. These infections can last longer or come back quickly after treatment. Fever and feeling run-down may accompany episodes.
Cough, chest pain, fever, and shortness of breath can signal lung infections. In complement component 3 deficiency, pneumonia can be more intense and sometimes requires hospital care. Recovery may take longer than usual.
Infection of the lining around the brain and spinal cord can occur. Warning signs include fever, severe headache, neck stiffness, vomiting, or confusion. Seek urgent medical care if these appear.
How people usually first notice Complement component 3 deficiency?
People often first notice complement component 3 (C3) deficiency after a child has unusually frequent or severe infections, especially with bacteria like Streptococcus pneumoniae or Neisseria meningitidis, sometimes leading to repeated ear, sinus, or lung infections or meningitis. Doctors may suspect it when standard vaccines don’t seem to protect well, infections keep coming back despite treatment, or blood tests show low C3 levels during an evaluation for recurrent infections or inflammation. In some, the first signs of complement component 3 deficiency are autoimmune-like features—such as rashes or joint pain—prompting testing that reveals how C3 is first noticed.
Types of Complement component 3 deficiency
Complement component 3 deficiency is a rare inherited immune condition with a few well-recognized clinical variants tied to how C3 is reduced or doesn’t function. These variants can influence how early infections start, how severe they are, and whether autoimmune features show up. Symptoms don’t always look the same for everyone. Understanding the main variants of C3 deficiency can help people and clinicians talk clearly about types of Complement component 3 deficiency and what to expect.
Complete C3 deficiency
C3 is essentially absent, and severe bacterial infections often begin in infancy or early childhood. People may have repeated ear, sinus, or bloodstream infections, especially with encapsulated bacteria like meningococcus and pneumococcus. Autoimmune features can occur but are less common than infections.
Partial C3 deficiency
C3 levels are low but not zero, so infections may start later and be somewhat less frequent. People often have milder, recurring respiratory or skin infections, with risk rising during stress or after viral illnesses. Autoimmune problems can still develop, depending on how low C3 runs over time.
Functional C3 defect
Total C3 may measure normal, but the protein does not work properly. Infections can resemble partial deficiency, and some may develop autoimmune features like lupus-like symptoms. Lab testing focused on complement function helps confirm this variant.
Secondary C3 consumption
C3 becomes low because it is constantly used up by another process, such as unchecked activation of the complement pathway. Symptoms track with the underlying driver and may include infections or inflammatory issues. Identifying and treating the cause can normalize C3 and distinguish it from primary types of Complement component 3 deficiency.
What genetics can tell you about symptoms
Certain C3 gene changes leave the immune “alarm system” quiet, so people have frequent, severe bacterial infections like pneumonia or meningitis, sometimes starting in infancy. Other variants tilt immunity toward misfires, raising risks of autoimmune problems such as lupus-like symptoms.
Causes and risk factors
Complement component 3 deficiency most often happens because both copies of the C3 gene have a change that stops the protein from working. Some risks are written in our DNA, passed down through families. Risk factors for Complement component 3 deficiency include having carrier parents, a known family history, or parents who are closely related. Other illnesses can lower C3 levels in the blood, but they do not cause this inherited deficiency. Vaccination status, exposure to germs, and other immune problems can shape how often infections happen, but they do not change the underlying genetic cause.
Environmental and biological risk factors
Complement component 3 deficiency can start from factors inside the body or from outside exposures that strain the immune system. Doctors often group risks into internal (biological) and external (environmental). People sometimes look up early symptoms of complement component 3 deficiency, but the drivers often begin with how much C3 your body can make and how quickly it’s used up. Below are key factors linked with a higher chance of low C3 levels.
New DNA changes become slightly more common as sperm-producing cells age. This slightly raises the chance a baby is born with complement component 3 deficiency.
The liver is still maturing, so C3 production can be lower at first. This can make complement component 3 deficiency more likely to be flagged on early tests, though levels may rise with age.
The liver makes most C3. Severe liver problems can reduce production and lead to low C3 levels. This can appear as complement component 3 deficiency on blood tests.
Conditions that form many immune complexes can use up C3 faster than it’s made. This can produce a temporary complement component 3 deficiency during flares.
Genetic risk factors
In families affected by Complement component 3 deficiency (C3 deficiency), the underlying issue is inherited changes in the C3 gene that reduce or stop production of a working C3 protein. Carrying a genetic change doesn’t guarantee the condition will appear. Understanding how it runs in families can guide targeted testing and, in some cases, support planning before early symptoms of complement component 3 deficiency are noticed.
C3 gene variants: Harmful changes in the C3 gene disrupt or prevent the C3 protein from working. This genetic loss is the direct cause of C3 deficiency.
Autosomal recessive: C3 deficiency develops when both copies of the C3 gene carry harmful changes. This pattern is known medically as autosomal recessive inheritance. If both parents are carriers, each pregnancy has a 25% (1 in 4) chance of an affected child.
Carrier status: People with one changed C3 gene are carriers and typically have no health problems from it. Carriers can pass the change to children. Some carriers have normal blood C3 levels, so only genetic testing can confirm carrier status.
Family history: Having a relative with C3 deficiency or a known C3 gene variant increases the chance of being a carrier. Targeted testing for the known family variant can clarify personal risk. This can guide reproductive planning.
Related parents: When parents share recent ancestors, they are more likely to carry the same rare C3 gene change. This raises the likelihood a child will inherit two copies and develop C3 deficiency. Genetic counseling can help families understand this pattern.
Variant severity: Different C3 gene changes can cause complete or partial deficiency. The exact variant can influence how low C3 levels are and the age at diagnosis.
Founder variants: In some families or communities, a single historical C3 gene change may be shared by many relatives. In these settings, carrier rates can be higher than in the general population. Testing can look for the specific founder variant if it is known.
Lifestyle risk factors
Complement component 3 deficiency is a genetic immune condition; lifestyle habits do not cause it. However, daily choices can influence infection risk, symptom flare-ups, and complications. Below are practical lifestyle risk factors for Complement component 3 deficiency and ways habits can help lower bacterial infection risk. This section highlights how lifestyle affects Complement component 3 deficiency in day-to-day life.
Keeping up with recommended vaccines and boosters reduces the chance that everyday exposures lead to severe infections. Consistent adherence supports your immune defenses that are otherwise compromised by low C3.
Rigorous handwashing and safe food handling lower exposure to bacteria that can cause serious infections in C3 deficiency. Avoiding raw or undercooked animal products can reduce gastrointestinal infections that may escalate quickly.
Twice-daily brushing, flossing, and regular dental cleanings reduce oral bacterial load. Lower oral bacterial burden means fewer opportunities for invasive infections and systemic inflammation in C3 deficiency.
Prompt cleansing and care of cuts, insect bites, and rashes limit bacterial entry points. Using clean dressings and seeking care for worsening redness or fever can prevent serious skin and soft tissue infections.
Risk prevention
Complement component 3 deficiency can’t be prevented outright, so the focus is on lowering infection risk and catching problems early. Prevention can mean both medical steps, like vaccines, and lifestyle steps, like everyday hygiene. Knowing the early symptoms of complement component 3 deficiency—like repeated ear, sinus, or lung infections—helps you act fast. Work with your care team to build a plan that fits your age, health history, and local infection risks.
Follow routine vaccines and make sure you get pneumococcal, meningococcal, Hib, and annual flu shots. Vaccines help reduce severe infections even when the immune system is weaker.
Your doctor may prescribe a daily antibiotic if you’ve had serious or frequent infections. This lowers the chance that bacteria gain a foothold.
Keep a plan for fevers or new infections, including when to start antibiotics and when to seek urgent care. Acting early can prevent complications in complement component 3 deficiency.
Ensure family members are fully vaccinated and stay home when sick. This reduces the germs you’re exposed to every day.
Transmission
Complement component 3 deficiency isn’t contagious—it doesn’t spread by coughing, touch, sex, or blood. It stems from changes in the C3 gene and is usually passed down in an autosomal recessive way, meaning a child needs two non-working copies to have the condition.
When both parents are healthy carriers, each pregnancy has a 25% (1 in 4) chance of a child with Complement component 3 deficiency, a 50% (1 in 2) chance of a carrier, and a 25% chance of neither copy being changed. This is how Complement component 3 deficiency is inherited, and relatives may consider carrier testing and genetic counseling.
When to test your genes
Complement component 3 deficiency is genetic, so consider testing if you’ve had recurrent, severe bacterial infections (especially with encapsulated bacteria), meningitis, or unusually poor responses to vaccines. Testing is also reasonable with a strong family history of complement deficiencies. Results can guide vaccines, antibiotics, and emergency plans.
Diagnosis
You might notice small changes in daily routines, like infections that linger or keep coming back despite treatment. Doctors usually begin with your story and a focused exam, then use stepwise tests to check how the complement system is working. When this pattern points to a complement issue, the genetic diagnosis of Complement component 3 deficiency is confirmed with specific blood tests and, when appropriate, DNA testing. Some diagnoses are clear after a single visit, while others take more time.
Recurrent, severe bacterial infections starting in childhood raise suspicion, especially ear, sinus, lung, blood, or brain infections. Slow recovery or frequent antibiotics can be clues. Skin infections and fever that escalates quickly are also common.
A detailed family and health history can help identify relatives with similar infections or early severe illness. Families with related parents or multiple affected siblings may have higher risk. This context guides which tests to run first.
CH50 and AH50 assays check how the classical and alternative complement pathways function. In Complement component 3 deficiency, both tests are typically very low or undetectable. Repeating testing when you’re well can avoid misleading results during active infection.
A quantitative C3 blood test is usually very low or absent in Complement component 3 deficiency. C4 and other complement components may be normal, helping narrow the cause. Levels are measured by standard immunology labs.
Stages of Complement component 3 deficiency
Complement component 3 deficiency does not have defined progression stages. It doesn’t typically move through set phases; instead, infections and complications can come in episodes that vary from person to person and across different ages. Early symptoms of complement component 3 deficiency often show up as repeated ear, sinus, or chest infections—especially in childhood—which can be the clue that leads to testing. Different tests may be suggested to help confirm the diagnosis and guide care, including blood tests that measure complement levels and function, and sometimes genetic testing to look for a cause.
Outlook and prognosis
Looking at the long-term picture can be helpful. For many people with Complement component 3 deficiency, infections start early in life and tend to be severe, especially from bacteria like pneumococcus and Haemophilus. Without consistent preventive care, repeated pneumonias, ear and sinus infections, bloodstream infections, or meningitis can lead to hospital stays and, in rare cases, life‑threatening complications. Doctors call this the prognosis—a medical word for likely outcomes.
With ongoing care, many people maintain good day‑to‑day health between infections. Preventive vaccines (including extra doses or specialized schedules), long‑term antibiotics when needed, and quick treatment at the first sign of fever can lower the risk of serious illness. Early symptoms of Complement component 3 deficiency can be subtle—frequent ear infections, slow recovery from colds, or unusual skin infections—so having a plan for rapid evaluation matters. Some also develop autoimmune problems over time, such as lupus‑like symptoms; these can usually be managed, but they add to the monitoring plan.
The outlook is not the same for everyone, but timely prevention and fast access to treatment are the biggest drivers of long‑term outcomes. Childhood and adolescence are typically the highest‑risk years; risk often continues into adulthood, so lifelong follow‑up is recommended. Mortality is mainly linked to overwhelming infections like meningitis or sepsis; in centers experienced with immunodeficiency care, this risk is substantially reduced. Talk with your doctor about what your personal outlook might look like, including tailored vaccines, emergency antibiotics at home, and when to seek urgent care for fever or severe symptoms.
Long-term effects
Living with Complement component 3 deficiency often means frequent, serious infections can leave lasting effects on the lungs, ears, and overall health. Many families first notice early symptoms of Complement component 3 deficiency as repeated pneumonia, ear infections, or bloodstream infections in infancy. Over years, risks also include autoimmune problems and kidney inflammation that can affect long-term health. Long-term effects vary widely, and some people remain relatively well between infections.
Frequent, severe bacterial infections can recur across childhood and adulthood. These often involve the lungs, ears, sinuses, or blood. Life-threatening infections like sepsis or meningitis can occur.
Repeated pneumonias can scar the airways and lead to bronchiectasis. This may cause a chronic cough and shortness of breath with activity. Lung function can gradually decline if infections continue.
Complement component 3 deficiency raises the chance of lupus-like illness and other autoimmune features. Joints, skin, or blood counts may be affected during flares. The pattern can shift over time.
In Complement component 3 deficiency, immune-complex glomerulonephritis can develop. Over years this may cause swelling, protein in the urine, and high blood pressure. Some people progress to chronic kidney disease.
How is it to live with Complement component 3 deficiency?
Living with complement component 3 (C3) deficiency often means planning around infection risk, especially from certain bacteria like Streptococcus pneumoniae and Neisseria meningitidis. Many people stay healthy day to day, but a fever, sore throat, or skin wound can’t be brushed off; prompt medical care, up‑to‑date vaccines, and sometimes preventive antibiotics become part of routine life. Travel, school, and work are all possible with forethought—carrying an emergency plan, knowing when to seek care, and telling close contacts what to watch for. Family members and partners may share in the vigilance, helping with reminders and quick decisions, but with good prevention and clear communication, most families find a steady rhythm that keeps life full and active.
Treatment and drugs
Complement component 3 deficiency is treated by lowering infection risk, preventing complications, and acting quickly when illness starts. Daily preventive antibiotics are often used, and many people receive extra protection with vaccines against bacteria that commonly cause severe infections, such as pneumococcal and meningococcal vaccines (with boosters as advised). Because infections can become serious quickly, doctors usually give a clear plan for urgent antibiotics at the first signs of fever, and some may prescribe standby antibiotics to start right away while seeking care. Treatment plans often combine several approaches, and regular follow‑up with an immunology or infectious disease specialist helps fine‑tune prevention, check for side effects, and update vaccines. For certain complications like autoimmune features, care may include medicines that calm the immune system, guided by a specialist.
Non-drug treatment
Complement component 3 deficiency raises the risk of serious, fast-moving infections, so day-to-day prevention and a clear action plan matter. Non-drug treatments often lay the foundation for staying well, with habits that cut exposure to germs and steps that speed care if symptoms start. These supports work alongside medical care to lower risk and to spot problems early. Not every approach works the same way for everyone, so your team may tailor these to your age, health, and infection history.
Wash hands often, especially before eating and after public transport. Use masks in crowded indoor spaces during outbreaks, and clean and cover cuts right away. Keep shared surfaces and devices clean.
Work with your clinician on exactly when to call, be seen, or go to urgent care for fever at or above 38.0°C (100.4°F). Learn the early symptoms of Complement component 3 deficiency infections, like severe headache, stiff neck, cough with fast breathing, or skin redness that spreads. Keep a written plan on the fridge and in your phone.
Breathing exercises and chest physiotherapy, taught by a respiratory therapist, can help move mucus after chest infections. This lowers the chance of mucus pooling that can set up new infections. Ask for training if you’ve had pneumonia or lingering cough with Complement component 3 deficiency.
Rinsing the nose with isotonic saline can ease congestion and help clear germs from the nasal passages. Use sterile or distilled water and clean devices carefully. This may reduce sinus infections in people with Complement component 3 deficiency.
Your genes may have an impact on how drugs work for you
Medicines for infections or inflammation can work differently in people with C3 deficiency because variations in immune genes change how the body recognizes germs and responds to treatment. Pharmacogenetics also matters: gene differences can alter drug breakdown, dosing needs, and side‑effect risk.
Pharmacological treatments
Medicines for complement component 3 deficiency focus on preventing and treating serious bacterial infections, especially from encapsulated germs like pneumococcus and meningococcus. Daily antibiotics and rapid treatment at the first sign of fever are common strategies. Alongside drug therapy, up-to-date vaccines and urgent medical review for fevers remain important. Plans are tailored by age, infection history, and local resistance patterns.
Penicillin V or amoxicillin taken every day can lower infection risk in complement component 3 deficiency. If you can’t take penicillin, azithromycin is a common alternative. Duration is individualized, often longer in childhood or during high‑risk periods.
Ceftriaxone given in the clinic or emergency department is widely used if there is sudden fever or concern for sepsis or meningitis. This rapid, broad coverage is important in complement component 3 deficiency. Go to emergency care immediately if fever develops.
Some specialists provide amoxicillin‑clavulanate (or a macrolide if allergic) to start while you head to urgent care. This does not replace hospital assessment, especially for early symptoms of complement component 3 deficiency like sudden fever, chills, or a new rash. Follow the plan your team gave you.
After close exposure to meningococcal disease, rifampin, ciprofloxacin, or ceftriaxone can be used to prevent illness. The choice depends on age, pregnancy, and local resistance patterns. Household contacts may also need prophylaxis.
Genetic influences
Most cases are caused by inherited changes in the C3 gene, which helps your immune system make the C3 protein that tags germs for removal. A change in a gene (mutation or variant) can sometimes affect health, and in complement component 3 deficiency it reduces or prevents C3 from working as it should. Complement component 3 deficiency is usually inherited in an autosomal recessive way—both copies of the C3 gene need a change for the condition to appear. If both parents carry one changed copy, each child has a 1 in 4 (25%) chance to be affected, a 1 in 2 (50%) chance to be a symptom‑free carrier, and a 1 in 4 (25%) chance to inherit two working copies. Carriers typically stay well, while people with complement component 3 deficiency often have very low C3 levels and a higher risk of certain infections; how severe this is can vary even within the same family. Genetic testing of the C3 gene, paired with genetic counseling, can clarify the genetic causes of complement component 3 deficiency and help guide care and family planning.
Is Complement component 3 deficiency genetic?
Genetics are central in Complement component 3 deficiency. Most cases arise from inherited C3 gene variants that reduce or disrupt C3 protein, raising infection risk. Family history matters; carriers may be healthy but can pass variants to children.
Pharmacogenetics—how genetics influence drug effects
Your specific C3 gene change shapes care by pointing doctors toward stronger infection prevention rather than changing most drug doses. People with Complement component 3 deficiency are more vulnerable to certain bacteria, so care plans often emphasize timely antibiotics and up-to-date vaccines against pneumococcal, meningococcal, and Hib infections. Conjugate vaccines are often used to build a stronger response, though protection is never relied on alone. Alongside your medical history and current infection, genetic testing can sometimes identify how your body handles certain medicines. For example, a well-known mitochondrial DNA change can raise the risk of permanent hearing loss with a class of antibiotics called aminoglycosides; if that risk is found, doctors may choose different drugs or monitor more closely. If a complement-blocking medicine is ever needed for another condition, the underlying complement weakness means extra steps—additional vaccines, preventive antibiotics, and closer follow-up—to lower infection risk. Other factors such as kidney and liver function, age, and the site of infection also guide antibiotic choice and dosing.
Interactions with other conditions
Infections from “encapsulated” bacteria can hit harder when Complement component 3 deficiency occurs alongside other issues that weaken defenses, such as a missing or removed spleen or sickle cell disease. Doctors call it a “comorbidity” when two conditions occur together, and in this case the pairing can mean more frequent pneumonia, sinus infections, or bloodstream infections and a higher chance of severe illness. Autoimmune conditions, especially lupus (systemic lupus erythematosus), are more common in people with Complement component 3 deficiency, and flares of one can aggravate the other, sometimes leading to kidney inflammation. Antibody problems (like common variable immunodeficiency) or long‑term lung disease can compound the risk of hard‑to‑clear infections, and certain immune‑targeting medicines may further increase vulnerability to specific bacteria. When another condition is present, early symptoms of Complement component 3 deficiency may show up sooner and more intensely, which is why coordinated care and up‑to‑date vaccines against pneumococcus, Haemophilus influenzae type b, and meningococcus are especially important.
How genes can cause diseases
Humans have more than 20,000 genes, each carrying out one or a few specific functions in the body. One gene instructs the body to digest lactose from milk, another tells the body how to build strong bones and another prevents the body's cells from beginning to multiply uncontrollably and developing into cancer. As all of these genes combined are the building instructions for our body, a defect in one of these genes can have severe health consequences.
Through decades of genetic research, we know the genetic code of any healthy/functional human gene. We have also identified that in certain positions on a gene, some individuals may have a different genetic letter from the one you have. We call these hotspots "Genetic Variations" or "Variants" in short. In many cases, studies have been able to show that having the genetic letter "G" in the position makes you healthy, but having the letter "A" in the same position disrupts the gene function and causes a disease. Genopedia allows you to view these variants in genes and summarizes all that we know from scientific research, which genetic letters (Genotype) have good or bad consequences on your health or on your traits.
History
Throughout history, people have described families where repeated, severe infections seemed to “run true,” especially in childhood. A toddler with pneumonia one winter, blood poisoning the next; a cousin with frequent ear infections that didn’t respond as expected. Long before lab tests, these patterns hinted that some immune defenses were missing or not working as they should.
From early theories to modern research, the story of complement component 3 deficiency moved from careful bedside observation to precise testing. In the mid‑20th century, clinicians recognized a group of conditions involving the “complement” system—proteins in the blood that help fight bacteria. Early case reports noted children with recurrent infections by certain bacteria and unusual reactions after infections, but the exact protein involved wasn’t always clear. As laboratory methods improved, scientists could measure individual complement proteins and saw that some people had very low or absent C3, a key hub protein that helps tag germs for removal.
Advances in genetics then connected the clinical picture to specific changes in the C3 gene. Researchers identified families in which C3 levels were consistently low across generations and linked this to inherited variants. This explained why some siblings shared a pattern of early, serious infections while others did not. It also clarified why complement component 3 deficiency could look different from person to person—some had mainly bacterial infections, while others also showed signs of immune overactivity, like inflammation in the kidneys.
In recent decades, awareness has grown as newborn screening panels, broader infectious disease workups, and specialized immunology clinics brought more people to testing earlier. With better vaccines, antibiotics, and preventive care, the course of complement component 3 deficiency has changed, too. Many living with the condition now have individualized plans to prevent and treat infections, and clinicians watch closely for complications that can be reduced with timely care.
Looking back helps explain why complement disorders were once considered rare and often missed: without specific tests, different complement problems could look alike, and infections were treated without searching for an underlying cause. Today, targeted blood tests and genetic studies can confirm complement component 3 deficiency, guide family counseling, and support practical steps to lower infection risk. Each stage in history has added to the picture we have today, turning family stories of “bad infections” into a clearly defined, manageable condition for many.