**Question:** In a completely and adequately immunized child against Diphtheria, the throat swab was collected. It showed the presence of Corynebacterium diphtheriae like organisms on Albee staining. These organisms can have one of the following properties on further laboratory processing -

A. Inability to produce toxin
B. Capability to produce toxin
C. Unable to cause disease
D. Unable to cause disease

**Core Concept:**

Diphtheria is a bacterial infection caused by Corynebacterium diphtheriae, which produces a toxin responsible for the symptoms and complications of the disease. In a fully immunized child, the presence of C. diphtheriae-like organisms on Albee staining indicates a false positive test due to cross-reactivity with other bacteria. Real diphtheria immunity is assessed by testing for serum neutralizing antibodies against the toxin.

**Why the Correct Answer is Right:**

In a fully immunized child, the correct answer should be:

B. Capability to produce toxin

This is because although the throat swab shows C. diphtheriae-like organisms on Albee staining, the child is fully immunized, indicating protection against the disease due to the presence of serum neutralizing antibodies against the toxin produced by C. diphtheriae. As a result, the false positive test result (A, C) would not represent the true state of the child's immunity. The correct assessment for immunity is through measuring toxin-neutralizing antibodies.

**Why Each Wrong Option is Incorrect:**

A. Unable to produce toxin - Incorrect because the false positive result indicates the presence of cross-reactive bacteria, not C. diphtheriae.
C. Unable to cause disease - Incorrect because the test result does not reflect the child's immunity status against diphtheria, which is determined by toxin-neutralizing antibodies.
D. Unable to cause disease - Similar to option C, this option is incorrect as it does not address the presence or absence of diphtheria immunity in the child.

**Clinical Pearl:**

In clinical practice, it is crucial to understand the limitations of a false positive diphtheria test result due to cross-reactivity with other bacteria. The true assessment of diphtheria immunity should rely on measuring toxin-neutralizing antibodies, not the test result itself. This knowledge is essential for proper disease diagnosis and treatment planning.