Meningococcal disease

Meningococcal disease is a serious, vaccine-preventable infection caused by Neisseria meningitidis, a gram-negative diplococcus bacterium also known as meningococcus. Meningococcal disease presents as life-threatening and rapidly progressive meningitis (infection of the protective membranes surrounding the brain and spinal cord), meningococcal septicemia (infection of the bloodstream), or a combination of both. Initial symptoms are flu-like and generally nonspecific, including fever, headache, neck stiffness, nausea, vomiting, and neurological symptoms including photophobia and confusion. A purple non-blanching rash may also be present. As infection progresses, septic shock eventually leads to gangrene and organ failure. Left untreated, meningococcal disease has an 80% mortality rate. With proper treatment, the mortality rate drops to 4–20%, with roughly 20% of survivors experiencing long-term complications including brain damage, blindness, deafness, and amputation. Neisseria meningitidis colonizes the nasopharynx of roughly 10% of the population without symptoms, but meningococcal disease can develop in rare cases when the bacteria enter the bloodstream. Meningococcal disease is transmitted by respiratory droplets or saliva from anyone who carries the bacteria in their respiratory tract, including asymptomatic individuals, although transmission usually requires close or lengthy contact. Symptoms usually begin three to four days after exposure. Almost all cases of meningococcal disease are caused by one of six encapsulated serotypes of N. meningitidis: A, B, C, W, X, and Y. Risk factors for infection include immunodeficiency, especially in cases of complement component deficiencies and low or absent spleen function. Diagnosis is often suspected based on symptoms and confirmed by culture or PCR finding N. meningitidis in the blood or cerebrospinal fluid. Several vaccines against meningococcal disease have been developed against all six disease-causing serotypes and have significantly reduced the incidence of disease. The United States CDC recommends the vaccine for all adolescents, along with children and adults at increased risk of infection. The World Health Organization recommends mass vaccination in areas with high rates of meningococcal disease. Meningococcal disease is treated with antibiotics; cephalosporins are generally the first-line treatment. In severe cases, additional supportive care may be necessary, and necrotic limbs may require amputation. In rarer cases, atypical presentation of meningococcal disease may occur in the form of pneumonia, septic arthritis, and other infections.

Predominant disease-causing serotypes differ by country and age group, with serotype B accounting for most new cases worldwide. Most cases in the developed world are sporadic, with outbreaks rarely occurring in residential settings such as college campuses. In the United States, incidence is highest among children under 5, young adults, and older adults. In some regions, such as the African meningitis belt, meningococcal disease is endemic and outbreaks are more frequent. In 2012, an estimated 1.2 million cases of meningococcal disease occurred worldwide, resulting in roughly 135,000 deaths.

Signs and symptoms

Meningococcal disease refers to a broad spectrum of conditions caused by invasive Neisseria meningitidis infection. It typically presents in two primary forms: meningitis and meningococcal septicemia. Meningitis is the most common presentation, representing roughly half of U.S. cases; in meningococcal meningitis, N. meningitidis invades the meninges, protective membranes surrounding the central nervous system. Meningococcal septicemia, in which N. meningitidis invades the bloodstream and triggers a life-threatening immune response known as sepsis, presents without meningitis in roughly 30% of U.S. cases. Many cases involve both meningitis and sepsis. Symptoms generally begin three to four days after exposure. Initial symptoms appear as flu-like illness, which can be problematic due to the necessity for prompt treatment. Meningococcal meningitis typically presents with sudden onset of fever, headache, neck stiffness, nausea, vomiting, and myalgia (muscle pain). Meningitis also causes neurological symptoms, including altered mental status and photophobia (sensitivity of the eyes to light). Kernig's sign and Brudziński's sign can confirm meningitis, but each have low sensitivities and cannot exclude illness. The classic "triad" of meningitis symptoms consists of fever, neck stiffness, and altered mental status; however, all three symptoms are present in less than half of meningitis cases. Infants may present with different symptoms, including inactivity, irritability, poor feeding, and abnormal reflexes. There may also be a bulge in the anterior fontanelle at the top of the head. Meningococcal septicemia, also known as meningococcemia, also causes flu-like symptoms that are difficult to differentiate from other illnesses. Initial symptoms of sepsis include fever, chills, diarrhea, nausea, vomiting, fatigue, and muscle and joint pain. Other common signs include hypotension (low blood pressure) and tachycardia (high heart rate). Another hallmark sign of meningococcal disease is bleeding under the skin, causing purple bruising known as petechiae (less than 3 mm in diameter) or purpura (3–10 mm). Bleeding under the skin can be confirmed if rolling a glass over the skin does not cause the rash to fade.

Complications Meningococcal disease is a rapidly progressive disease, and without treatment can quickly lead to extensive complications. Even with treatment, one in five survivors experience long-term complications. Like other gram-negative infections, N. meningitidis releases endotoxin, causing disseminated intravascular coagulation (DIC), a condition in which blood clots block small blood vessels. As available clotting factors are used up, bleeding occurs throughout the body and blood vessels are damaged. Sepsis eventually leads to tissue death (necrosis) and organ failure throughout the body. Tissue death is most common in the limbs, which may require amputation after treatment. If hemorrhaging affects the adrenal glands, Waterhouse–Friderichsen syndrome can occur, causing deadly adrenal insufficiency. Meningitis may cause irreversible brain damage, blindness, deafness, and other neurological problems.

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