Any time there is an outbreak of an infectious disease, the public generally wants to know how common it is and what their risk of getting it is. Journalists will want to stay on top of new and continuing cases as well, but to provide context to those stories, or to others about infectious diseases or vaccines, they may want information on historical incidence or trends as well. Below are resources for infectious diseases exclusively within the U.S.
Domestically, the Centers for Disease Control and Prevention maintain a National Notifiable Diseases Surveillance System (NNDSS) that tracks all Nationally Notifiable Conditions, diseases which health departments are required to report when they have a local case with the condition. (Clicking on each disease tells you the case definition and how long it has been a notifiable condition.) This spreadsheet tells you whether a disease was reported during each of the years included. These diseases are reported for the week, month and year-to-date in each Morbidity and Mortality Weekly Report. To see how many cases have been reported during a particular month or up through the year-to-date, look for the Notifiable Diseases and Mortality Tables link for the month and year you need from 2015 or 2016. The CDC also provides MMWR summaries of cases for nationally notifiable conditions during each past year back to 1993. Be sure to read what data users should know about the National Notifiable Diseases Surveillance System before you dig into the data, and definitions of key terms are available here. Other helpful information to understanding the system is here.
You can also look up state level data on specific notifiable diseases, and other data from the NNDSS can be accessed here, part of the CDC’s overall data site. The State Health Statisticpage of the MMWRs contains links to the MMWR Notifiable Diseases Data Tables, NNDSS Morbidity Tables, and Mortality Tables by week, year, and any of 122 cities. You may also find helpful information from specific data sets in the CDC’s Wide-ranging Online Data for Epidemiologic Research (WONDER).
Influenza is tracked through the extensive and granular Weekly U.S. Influenza Surveillance Report (FluView). For emerging viruses, the CDC will often set up a disease-specific page as they did for MERS, SARS and Zika, whose U.S. cases are tracked here.
You can query specific data sets for HIV/AIDS, hepatitis, sexually transmitted diseases and tuberculosis at the The National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention (NCHHSTP) Atlas. The National Center for Health Statistics has links for tracking new annual tuberculosis, salmonella, Lyme and meningococcal cases as well as trends and data for AIDS/HIV, influenza, measles, pneumonia, sexually transmitted diseases, viral hepatitis and whooping cough/pertussis. Most vaccine-preventable diseases have their own pages for trends and historical data, such as a page for measles and one for pertussis. (Frustratingly, it can sometimes be difficult to find precisely the information you need. This table of pertussiscases by year historically is not accessible from the main pertussis page or pertussis surveillance page for some reason.)