A child presents with a white patch over the tonsils, diagnosis is best made by culture in –
**Core Concept**
The diagnosis is likely a case of diphtheria, a bacterial infection caused by Corynebacterium diphtheriae. This bacterium produces a toxin that leads to tissue damage and necrosis, resulting in a characteristic white patch over the tonsils.
**Why the Correct Answer is Right**
The correct answer is best determined by culturing the bacteria from a throat swab. Diphtheria toxin is produced by the bacteria, and the culture will reveal the presence of Corynebacterium diphtheriae. The culture is the gold standard for diagnosis, as it can distinguish between diphtheria and other similar infections. The bacteria can be identified under a microscope, and further tests can be conducted to confirm the presence of the toxin.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while a throat swab can be used to collect a specimen for culture, it is not the best method for diagnosing diphtheria. A throat swab may not provide an accurate sample, and other methods such as a nasopharyngeal swab are more effective.
**Option B:** This option is incorrect because a rapid streptococcal test is used to diagnose streptococcal infections, not diphtheria. While diphtheria can be confused with streptococcal infections, a rapid streptococcal test will not provide a definitive diagnosis.
**Option C:** This option is incorrect because a Gram stain can be used to identify the presence of bacteria, but it cannot distinguish between different types of bacteria. A Gram stain may show the presence of Gram-positive rods, but it will not confirm the presence of Corynebacterium diphtheriae.
**Option D:** This option is incorrect because a blood culture is used to diagnose bacterial infections that have entered the bloodstream, such as sepsis. While a blood culture may show the presence of bacteria, it is not the best method for diagnosing diphtheria.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that diphtheria can be confused with other infections, such as streptococcal infections. A throat swab should be sent for culture to confirm the diagnosis, as the clinical presentation alone may not be sufficient to make a definitive diagnosis.
**Correct Answer:** B. A rapid streptococcal test.