Public Health Surveillance, X-Linked Disorders, and Transfusion Reactions

This set covers public health surveillance methods, X-linked genetic disorders, and the various types and management of transfusion reactions.

Public Health Surveillance

The ongoing, systematic collection, analysis, interpretation, and timely dissemination of health data to support public health action.

Incidence

A measure of new cases within a population at risk, calculated as $\text{Incidence} = \frac{\text{New Cases}}{\text{Population at Risk}}$; used to detect trends and identify outbreaks.

Prevalence

A measure of all existing cases within a total population, calculated as $\text{Prevalence} = \frac{\text{Existing Cases}}{\text{Total Population}}$; used to determine disease burden and healthcare planning.

Passive Surveillance

A surveillance type where providers report cases routinely; characterized by low cost but a limitation of underreporting.

Active Surveillance

A surveillance type where public health officials actively search for cases, providing high sensitivity though it is expensive.

Sentinel Surveillance

A surveillance type where selected sites report data, providing good trend monitoring without providing full coverage of the population.

Syndromic Surveillance

A surveillance method using symptom patterns, such as ED visits, to provide the fastest early warning, though it is non-specific.

Sensitivity

The ability of a test to correctly identify diseased individuals; high sensitivity yields few false negatives.

Specificity

The ability of a test to correctly identify healthy individuals; high specificity yields few false positives.

Positive Predictive Value (PPV)

The probability that a positive result is truly positive; this value decreases in low prevalence settings, leading to more false positives.

Timeliness

A data quality attribute indicating that surveillance data is available quickly enough to support public health action.

X-Linked Recessive Inheritance

A pattern of inheritance where males are usually affected because they have only one X chromosome, and there is no male-to-male transmission.

X-Inactivation (Lyonization)

The random inactivation of one X chromosome in females, resulting in mosaicism; carrier females may show symptoms if the normal X is preferentially inactivated.

Hemophilia A

A genetic disorder caused by a deficiency in Factor VIII due to a mutation in the $F8$ gene, characterized by prolonged bleeding and hemarthrosis.

Hemophilia B

A genetic disorder caused by a deficiency in Factor IX due to a mutation in the $F9$ gene, with findings similar to Hemophilia A.

Duchenne Muscular Dystrophy (DMD)

An X-linked disorder caused by mutations in the $DMD$ gene, resulting in progressive muscle weakness and early childhood onset primarily in boys.

aPTT (Activated Partial Thromboplastin Time)

A screening test that is prolonged in Hemophilia A and B, typically found alongside a normal PT.

Variant of Uncertain Significance (VUS)

An ACMG variant classification that should not be used alone for major clinical decisions.

Acute Hemolytic Transfusion Reaction (AHTR)

A potentially fatal reaction occurring within $24$ hours of transfusion, caused by ABO incompatibility and marked by fever, flank pain, and hemoglobinuria.

Febrile Nonhemolytic Reaction

The most common transfusion reaction, caused by cytokines or leukocyte antibodies; characterized by fever and chills after ruling out hemolysis.

Delayed Hemolytic Reaction

A reaction occurring days to weeks after transfusion due to alloantibodies against minor antigens, characterized by falling hemoglobin and a positive DAT.

Transfusion-Related Acute Lung Injury (TRALI)

An immune-mediated reaction occurring within $6$ hours of transfusion where donor antibodies activate recipient neutrophils, causing acute respiratory distress and normal or low blood pressure.

Transfusion-Associated Circulatory Overload (TACO)

A reaction caused by volume overload during or after transfusion, characterized by dyspnea, hypertension, and a positive response to diuretics.

Hemovigilance

The continuous monitoring and reporting of transfusion-related adverse events to improve safety and identify trends.