Mumps

==Epidemiology==

=== Clinical age and immunity ===
Mumps is found worldwide.<ref name="davison" /> In the absence of vaccination against mumps there are between 100 and 1,000 cases per 100,000 people each year, i.e. 0.1% to 1.0% of the population are infected each year. The number of cases peaks every 2–5 years,<ref name="who" /> with incidence highest in children 5–9 years old.<ref name="shu" /> According to seroconversion surveys done prior to the start of mumps vaccination, a sharp increase in mumps antibody levels at age 2–3 was observed.

Furthermore, 50% of 4–6 year olds, 90% of 14–15 year olds, and 95% of adults had tested positive to prior exposure to mumps, indicating that nearly all people are eventually infected in unvaccinated populations.<ref name="su" /><ref name="rubin" />

Prior to the start of vaccination, mumps accounted for ten percent of meningitis cases and about a third of encephalitis cases.<ref name="cdc" /> Worldwide, mumps is the most common cause of inflammation of the salivary glands.<ref name="kessler" /> In children, mumps is the most common cause of [[deafness]] in one ear in cases when the inner ear is damaged.<ref name="rubin" /> Asymptomatic infections are more common in adults,<ref name="who" /> and the rate of asymptomatic infections is very high, up to two-thirds, in vaccinated populations. Mumps vaccination has the effect of increasing the average age of the infected in vaccinated populations that have not previously experienced a mumps outbreak.<ref name="beleni" /> While infection rates appear to be the same in males and females, males appear to experience symptoms and complications, including neurological involvement, at a higher rate than females.<ref name="su" /><ref name="junghanss" />{{Primary source inline|date=November 2021}} Symptoms are more severe in adolescents and adults than in children.<ref name="senanayake" />

=== Settings of outbreaks ===
It is common for outbreaks of mumps to occur. These outbreaks typically occur in crowded spaces where the virus can spread from person to person easily, such as schools, military barracks, prisons, and sports clubs.<ref name=su /><ref name=davis /> Since the introduction of vaccines, the frequency of mumps has declined dramatically, as have complications caused by mumps. The epidemiology in countries that vaccinate reflects the number doses administered, age at vaccination, and vaccination rates. If vaccine coverage is insufficient, then herd immunity may be unobtainable and the average age of infection will increase, leading to an increase in the prevalence of complications. Risk factors include age, exposure to a person with mumps, compromised immunity, time of year, travel history, and vaccination status.<ref name=su /> Mumps vaccination is less common in developing countries, which consequently have higher rates of mumps.<ref name=junghanss />

Cases peak in different seasons of the year in different regions. In temperate climates, cases peak in winter and spring, whereas in tropical regions no seasonality is observed.<ref name=beleni /> Additional research has shown that mumps increases in frequency as temperature and humidity increase. The seasonality of mumps is thought to be caused by several factors: fluctuation in the human immune response due to seasonal factors, such as changes in [[melatonin]] levels; behavior and lifestyle changes, such as school attendance and indoor crowding; and meteorological factors such as changes in temperature, brightness, wind, and humidity.<ref name=su />
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