Many different viruses can cause meningitis. About 90% of cases of viral meningitis are caused by members of a group of viruses known as enteroviruses, such as coxsackieviruses and echoviruses. These viruses are more common during summer and fall months. Herpesviruses and the mumps virus can also cause viral meningitis.
Many of the bacteria and viruses that cause meningitis are fairly common and are typically associated with other routine illnesses. Bacteria and viruses that infect the skin, urinary system, gastrointestinal or respiratory tract can spread by the bloodstream to the meninges through cerebrospinal fluid, the fluid that circulates in and around the spinal cord.
Viral meningitis is caused by any of a number of different viruses, many of which are associated with other diseases. About half of the cases in the United States are caused by common intestinal viruses. Occasionally, children with mumps or herpes virus infection develop viral meningitis. Mosquito-borne viruses also cause some cases each year. In many cases, a specific virus cannot be identified.
In some cases of bacterial meningitis, the bacteria spread to the meninges from a severe head trauma or a severe local infection, such as a serious ear infection (otitis media) or nasal sinus infection (sinusitis).
Many different types of bacteria can cause bacterial meningitis. In newborns, the most common causes are Group B streptococcus, Escherichia coli, and Listeria monocytogenes. In older kids, Streptococcus pneumoniae (pneumococcus) and Neisseria meningitidis (meningococcus) are more often the causes.
Another bacteria, Haemophilus influenza type b (Hib), can also cause the illness but because of widespread childhood immunization, these cases are now rarer.
Similarly, many different viruses can lead to viral meningitis, including enteroviruses (such as coxsackievirus, poliovirus, and hepatitis A) and the herpesvirus.
