The viridans are normal inhabitants of the body and are usually harmless; however, they can contribute to tooth decay. Streptococcus pneumoniae is the most common cause of otitis media in children. It can also cause meningitis and pneumonia. The S. pneumoniae diseases are sometimes referred to as pneumococcal diseases. The development of drug-resistant strains of pneumococci has caused concern in the medical community. Vaccination against pneumococcal pneumonia is recommended for very young children and older persons; the vaccine inoculates against the most prevalent strains of S. pneumoniae.