Epidemic Incidence per 100k

Epidemiological Incidence Rate

Incidence tells you how fast new cases of a disease show up in a population over a set window of time, whether that window is a year, a month or a single week. You compute it with incidence = new_cases / population_at_risk × 100,000. Expressing the result per 100,000 inhabitants is what lets you put regions of very different sizes side by side.

Prevalence and incidence are not the same thing. Where prevalence counts the total burden, incidence captures the force of an outbreak, the answer to “how quickly is this disease spreading?” When the incidence curve climbs, transmission is active or some new risk factor has appeared. When it drops, your control measures are doing their job.

Applications

It is one of the workhorses of public-health surveillance, tracked for dengue, COVID-19, measles, tuberculosis, foodborne outbreaks and workplace injuries alike. In Brazil the SUS SINAN (Sistema de Informação de Agravos de Notificação) gathers the compulsory notifications, while bodies such as CONASS and CONASEMS roll the state and municipal rates up into figures that feed policy.

FAQ

What's the difference between incidence and prevalence? Incidence only counts the new cases that arise during a period. Prevalence counts every existing case at a given moment, the chronic ones included.

Why multiply by 100,000? It is the conventional base, and for most diseases it lands on whole numbers that are easy to read. Rare events like cancer subtypes are usually quoted per million, and very common conditions often work fine per 1,000.

What is the “population at risk”? Only the people who could actually catch the disease during the period. For a vaccine-preventable illness you would leave the immunized out, and for cervical cancer you would count women only.