Topic
Infection and immunity
How infections, vaccines, and the immune system work, and how the evidence behind them is judged.
This page collects every article by Dr. Damon Tojjar in this topic. For all topics see browse by topic, and for the source-anchored record see damontojjar.com/record.
Articles in this topic (22)
- What a Positive Antibody Test Does and Does Not Tell You About Immunity
A positive antibody test tells you that your immune system has met a pathogen or a vaccine antigen and produced antibodies against it. It does not tell you that you...
- When a Urinary Bug Is Not a UTI: The Case Against Treating Asymptomatic Bacteriuria
Bacteria in the urine are not the same thing as a urinary tract infection. When someone has no urinary symptoms, a positive culture usually reflects asymptomatic...
- C. diff Testing: Why a Positive PCR Does Not Always Mean Infection
A positive Clostridioides difficile PCR test tells you that bacteria carrying the toxin gene are present in a stool sample. It does not tell you that those bacteria...
- From Stool Transplant to Approved Product: Microbiome Therapy Evidence in Recurrent C. diff
Recurrent Clostridioides difficile infection now has two FDA-approved microbiome medicines, and both trace directly back to fecal microbiota transplantation (FMT)....
- The Math Behind Herd Immunity and Why the Threshold Is Not One Number
The herd immunity threshold is not a fixed percentage. It is the output of a short formula, 1 minus 1/R0, that climbs as a pathogen becomes more transmissible,...
- How Antibiotic Resistance Emerges and What Stewardship Actually Does
Antibiotic resistance is not a mysterious force. It emerges through ordinary natural selection: an antibiotic kills the susceptible bacteria in a population and...
- How Each Year's Flu Vaccine Strains Are Chosen and Why the Match Varies
Every year, the flu shot is a forecast. Roughly six months before a season starts, the World Health Organization examines global surveillance data and names the...
- How We Know HIV PrEP Works and Why Adherence Changes the Number
The headline that pre-exposure prophylaxis is about 99 percent effective is accurate, but it describes a specific condition: the medicine being present in the body...
- Reading an Outbreak: Case Definitions, Attack Rates and the Epidemic Curve
Field epidemiology reads an outbreak with three linked tools. A case definition decides who counts, an attack rate measures illness among the exposed, and the...
- How Vaccine Safety Is Monitored and Why VAERS Numbers Are Misread
Vaccine safety monitoring in the United States runs on two different kinds of systems, and confusing them is the most common way VAERS numbers get misread. The...
- Innate vs Adaptive Immunity: The Two Defense Systems and How They Divide Labor
Your body defends itself with two immune systems that run on different clocks and different rules. The innate system reacts within minutes to hours, using a fixed...
- Latent vs Active TB: What a Positive Skin Test or IGRA Really Tells You
A positive tuberculin skin test or IGRA tells you one thing with confidence: your immune system has met Mycobacterium tuberculosis and remembers it. It does not...
- Why One Positive Lyme Test Is Not a Diagnosis: Two-Tier Serology Explained
A single positive result is a starting point, not a verdictOne positive Lyme antibody test does not establish that a person has Lyme disease. The CDC recommends a...
- Passive Immunity: How Monoclonal Antibodies Protect Without Training the Immune System
Passive immunity is protection you receive ready-made. Instead of teaching the immune system to build its own antibodies, a clinician administers antibodies...
- Rapid Antigen vs PCR: Why the Same Person Can Test Both Ways
A person really can be positive on a PCR test and negative on a rapid antigen test at the same moment, and in most cases neither result is wrong. The two tests...
- Sepsis Versus Infection: What the Sepsis-3 Definition Changed
Sepsis-3, the 2016 international consensus published in JAMA by Singer and colleagues, redefined sepsis as "life-threatening organ dysfunction caused by a...
- Why Shorter Antibiotic Courses Are Often as Good as Longer Ones
For a growing list of common bacterial infections, randomized trials show that shorter antibiotic courses work about as well as the longer ones clinicians...
- Why a Positive Test Means Different Things in Different Populations
A positive test result is not a fixed fact about a person. The same test, run the same way in the same laboratory, points to disease with very different confidence...
- Undetectable Equals Untransmittable: The Evidence Behind U Equals U
Undetectable equals untransmittable, or U=U, means that a person living with HIV who takes antiretroviral therapy and keeps a durably suppressed viral load does not...
- Vaccine Efficacy vs Effectiveness: What the Percentages Actually Measure
Efficacy and effectiveness sound interchangeable, but they describe a vaccine's performance under two very different conditions. Efficacy is the risk reduction...
- What Susceptible and Resistant Mean on a Culture Report
The short versionWhen a culture report calls an organism "susceptible" or "resistant," it is not naming a fixed property of the microbe. It is reporting a...
- What a Correlate of Protection Is and Why It Speeds Vaccine Decisions
A correlate of protection is a measurable immune marker, usually an antibody level, that reliably predicts whether a vaccinated person is protected against a...