Infection, immunity, and cancer
Outpatient Cellulitis: Purulent Versus Nonpurulent Skin Infection
How the purulent versus nonpurulent split sorts skin infections, why it guides antibiotic choice, and the red flags that mean urgent care.
Health & Evidence Library
Infection, immunity, and cancer
Guides to infection, antimicrobial reasoning, immune response, screening, cancer evidence, and treatment-related questions.
38 guides · Page 1 of 1
Infection, immunity, and cancer
Acute Sinus Symptoms and the Antibiotic Question
Most sinus infections are viral and clear without antibiotics. Learn the viral vs bacterial clues, the 10-day rule, and what actually relieves symptoms.
Infection, immunity, and cancer
Strep Throat or a Viral Sore Throat? Reading the Centor Score
Most sore throats are viral. The Centor (McIsaac) score estimates strep odds and when a throat swab or antibiotics are actually worth it.
Infection, immunity, and cancer
What Tumor Mutational Burden Does and Does Not Tell You
Tumor mutational burden counts selected mutations per megabase. It can inform immunotherapy choices, but platform and tumor context matter.
Infection, immunity, and cancer
What Antibiotic Susceptible and Resistant Mean: MIC Explained
Learn how laboratories measure MIC, apply breakpoints, and report susceptible, intermediate, or resistant results, plus the limits of an antibiogram.
Infection, immunity, and cancer
What a Vaccine Correlate of Protection Is
A vaccine correlate of protection links an immune marker with reduced risk. Learn the evidence needed, how correlates speed decisions, and their limits.
Infection, immunity, and cancer
What a Tumor-Agnostic Approval Means
A tumor-agnostic approval targets a molecular feature across specified cancers, not every tumor. Learn how basket trials, testing, labels, and uncertainty fit.
Infection, immunity, and cancer
Vaccine Efficacy vs Effectiveness: How Each Is Measured
Vaccine efficacy measures relative risk reduction in a trial; effectiveness estimates performance in practice. Learn the designs, endpoints, biases, and limits.
Infection, immunity, and cancer
Undetectable Equals Untransmittable: The Evidence
U=U means sustained HIV viral suppression prevents sexual transmission. Learn what the studies showed, what undetectable means, and the message's boundaries.
Infection, immunity, and cancer
Why Shorter Antibiotic Courses Are Often Enough
Trials support shorter antibiotic courses for selected infections, but the right duration depends on diagnosis, source control, response, and host risk.
Infection, immunity, and cancer
Why a Test's Positive Predictive Value Depends on Prevalence
A positive test can mean very different things in low-risk and high-risk groups. Learn how prevalence, pretest probability, and false positives shape PPV.
Infection, immunity, and cancer
Sepsis Versus Infection: What Sepsis-3 Changed
Sepsis-3 centers life-threatening organ dysfunction, not infection alone. Learn how SOFA, qSOFA, SIRS, and septic shock fit current evidence.
Infection, immunity, and cancer
Rapid Antigen vs PCR: Why the Same Person Can Test Both Ways
How antigen and molecular tests detect viruses, why results can disagree, and how timing, symptoms, specimens, and purpose change interpretation.
Infection, immunity, and cancer
Why One Positive Lyme Test Is Not a Diagnosis: Two-Tier Serology Explained
How two-tier Lyme serology works, why antibody tests miss early infection and stay positive after treatment, and why testing low-risk patients misleads.
Infection, immunity, and cancer
What a Positive Antibody Test Does and Does Not Tell You About Immunity
FDA and CDC say a positive antibody test records prior contact with a pathogen, not immunity. Here is how it differs from a validated correlate of protection.
Infection, immunity, and cancer
The Math Behind Herd Immunity and Why the Threshold Is Not One Number
Herd immunity has no single threshold. The 1 minus 1/R0 formula rises with transmissibility, and its assumptions rarely hold in the real world.
Infection, immunity, and cancer
Reading the Numbers on Approved Microbiome Medicines for Recurrent C. diff
Recurrent C. diff now has two FDA-approved microbiome products. Here is what Rebyota and Vowst do, and how to read their trial results honestly.
Infection, immunity, and cancer
Passive Immunity: How Monoclonal Antibodies Protect Without Training the Immune System
How preformed antibodies like palivizumab and nirsevimab give immediate, temporary RSV protection, and how that differs from a vaccine.
Infection, immunity, and cancer
Multi-Cancer Early Detection Blood Tests and What the Evidence Shows
What multi-cancer early detection blood tests measure, why a randomized mortality trial is the real test, and the open overdiagnosis questions.
Infection, immunity, and cancer
Lynch Syndrome and Why Tumors Are Screened Universally
Why every colorectal and endometrial tumor is tested for mismatch repair loss to catch inherited Lynch syndrome, and how the specific gene guides surveillance.
Infection, immunity, and cancer
Latent vs Active TB: What a Positive Skin Test or IGRA Really Tells You
A positive TB skin test or IGRA proves immune memory, not live disease. Here is why the test cannot tell latent from active, and how risk is judged.
Infection, immunity, and cancer
Innate vs Adaptive Immunity: The Two Defense Systems and How They Divide Labor
Innate immunity reacts in hours with fixed receptors and no memory; adaptive immunity takes days but learns a specific pathogen and remembers it.
Infection, immunity, and cancer
How We Know HIV PrEP Works and Why Adherence Changes the Number
Why PrEP's roughly 99 percent figure depends on the drug being present in the body, and how trials from iPrEx to lenacapavir proved it.
Infection, immunity, and cancer
How Vaccine Safety Is Monitored and Why VAERS Numbers Are Misread
Why a raw VAERS report count cannot prove a vaccine caused harm, and how controlled systems like the Vaccine Safety Datalink actually measure risk.
Infection, immunity, and cancer
How the Lung Cancer Screening Guideline Was Built
How USPSTF set the age and pack-year rules for low-dose CT lung screening by weighing lives saved against false positives and overdiagnosis.
Infection, immunity, and cancer
How the Colorectal Screening Guideline Weighs Colonoscopy Against Stool Tests
Why the USPSTF lowered the colorectal screening start age to 45 and how it compares colonoscopy, FIT, and stool-DNA without naming one best test.
Infection, immunity, and cancer
How MSI-High and Mismatch Repair Testing Guides Immunotherapy
Why MSI-High and mismatch repair deficiency predict immunotherapy response, and how they became the first marker used to approve a drug across any solid tumor.
Infection, immunity, and cancer
How Investigators Read an Outbreak: Case Definitions, Attack Rates, and the Epidemic Curve
A plain-language guide to the three tools field epidemiologists use to read an outbreak, and the built-in blind spot in each.
Infection, immunity, and cancer
How Immune Checkpoint Inhibitors Work and Why Response Is Uneven
How PD-1, PD-L1, and CTLA-4 blockade release the immune system's brakes, and an evidence-based look at why only some tumors respond.
Infection, immunity, and cancer
How Each Year's Flu Vaccine Strains Are Chosen and Why the Match Varies
How flu vaccine strains are picked months ahead, why antigenic drift causes mismatch, and how to read a low-effectiveness season.
Infection, immunity, and cancer
How CAR T Cell Therapy Works, and Why Its Risks Come Built In
How CAR T therapy reprograms a patient's own T cells against CD19 or BCMA, and why cytokine release syndrome and ICANS are mechanism-linked.
Infection, immunity, and cancer
How Cancer Staging Works and Why Stage Predicts Outcome
How the TNM system and AJCC prognostic stage groups turn tumor size, node spread, grade, and biomarkers into a survival estimate.
Infection, immunity, and cancer
How Antibiotic Resistance Emerges and What Stewardship Actually Does
Why antibiotic resistance is a selection problem, how the CDC ranks the threats, and what controlled evidence says stewardship achieves.
Infection, immunity, and cancer
How a Screening Guideline Is Built: The Case of Mammography at 40
A plain-language look at how the USPSTF turned limited trials and six simulation models into its 2024 Grade B call for mammography every two years from age 40.
Infection, immunity, and cancer
Hereditary Cancer Risk and What BRCA Testing Can Tell You
BRCA testing is the end of a path, not a general screen. How a risk tool, counseling, and a result each answer a different question.
Infection, immunity, and cancer
Cancer Screening: Weighing Earlier Detection Against Overdiagnosis
Why cancer screening trades earlier detection for overdiagnosis, and how mortality trials, not survival figures, reveal which programs truly help.
Infection, immunity, and cancer
C. diff Testing: Why a Positive PCR Does Not Always Mean Infection
A positive C. difficile PCR can signal carriage rather than disease; smart test selection plus toxin confirmation curbs overdiagnosis.
Infection, immunity, and cancer
Bacteria in the Urine Without Symptoms: Why the Answer Is Usually to Do Nothing
A positive urine culture without symptoms is asymptomatic bacteriuria, not a UTI. Guidelines say leave it alone, apart from two exceptions.