What statement is true regarding Haemophilus influenzae infections?

The statement that invasive infections of Haemophilus influenzae are most commonly associated with encapsulated strains is accurate because encapsulated strains of this bacterium, particularly type b (Hib), possess a polysaccharide capsule that protects them from phagocytosis by immune cells. This enhances their virulence and ability to cause serious infections such as meningitis, pneumonia, and epiglottitis, especially in young children who are more vulnerable due to an underdeveloped immune system.

In contrast, non-encapsulated strains generally do not cause severe disease and are part of the normal flora in the upper respiratory tract. The presence of the capsule is a critical factor in the pathogenicity of H. influenzae, making encapsulated strains the primary culprits in invasive disease. Understanding this relationship helps in grasping why vaccination against Hib has significantly reduced the incidence of invasive infections in populations that are routinely immunized.