Before administering cefazolin (Ancef), the nurse checks for a previous allergic reaction to:

A. "Are you having any difficulty breathing?":

Difficulty breathing is a critical symptom that may indicate a severe allergic reaction, such as anaphylaxis, which can be life-threatening. It is essential to assess for difficulty breathing immediately as it requires urgent intervention to ensure the patient's airway is clear and to administer appropriate treatment.

B. "Have you noticed any blood in your stool?":

While blood in the stool could indicate gastrointestinal bleeding, it is not typically associated with allergic reactions to antibiotics. This symptom is more commonly associated with other conditions such as gastrointestinal ulcers, infections, or inflammatory bowel disease. While important to assess, it is not as immediately concerning as difficulty breathing in the context of a suspected allergic reaction.

C. "Are you having difficulty with your hearing?":

Difficulty with hearing is not a common symptom of allergic reactions to antibiotics. It may be associated with other conditions such as ear infections or ototoxicity from certain medications. While it is important to assess any changes in hearing, it is not typically an immediate concern in the context of a suspected allergic reaction.

D. "Do you have a headache?":

Headaches are a common symptom that can occur for various reasons, including stress, tension, dehydration, or as a side effect of medications. While headaches can sometimes occur as a side effect of certain drugs, they are not typically associated with severe allergic reactions such as anaphylaxis. Therefore, while it is important to assess for headaches, it is not as immediately concerning as difficulty breathing in the context of a suspected allergic reaction.

A. Substance that can inhibit the growth of bacteria:

This definition is incorrect. The term "virulence" does not refer to a substance that inhibits bacterial growth. Instead, it pertains to the ability of a microorganism to cause disease.

B. Permanent, inheritable changes to DNA:

This definition is incorrect. Permanent, inheritable changes to DNA are typically referred to as mutations. While mutations can impact the characteristics of microorganisms, the term "virulence" specifically relates to disease-causing ability rather than genetic changes.

C. When a microbe is no longer affected by a drug following treatment with anti-infectives:

This definition is incorrect. The phenomenon described here is known as drug resistance or antimicrobial resistance. It refers to the ability of microorganisms to survive and multiply in the presence of antimicrobial agents, rendering the drugs ineffective.

D. The severity of disease that an organism is able to cause:

This definition is correct. Virulence refers to the degree or severity of disease that an organism, such as a bacterium or virus, is capable of causing. Microorganisms with high virulence can cause severe illness or death in infected hosts, while those with low virulence may cause milder symptoms or no symptoms at all.