epidemiology {ep´ï-de´me-ol´o-je} 1. the study of the relationships of the various factors determining the frequency and distribution of diseases in human communities. 2. the field of medicine concerned with the determination of the specific causes of localized outbreaks of infection, such as hepatitis, of toxic disorders, such as lead poisoning, or any other disease of recognized etiology. — Dorland’s Medical Dictionary


Influenza is commonly referred to as “the flu.” It is a contagious respiratory illness caused by influenza viruses that affect the nose, throat, and lungs. There are two main types of influenza virus: A and B. Each type includes many different strains that tend to change from year to year.

In the United States, influenza occurs most often in the late fall and winter months.  Anyone can get influenza, but it is more likely to cause serious illness in young children, pregnant women, older persons, people with chronic illnesses (e.g., lung disease, heart disease, cancer, or diabetes) or those with weakened immune systems.

Influenza spreads mainly by droplets from the nose or throat that are released when an infected person coughs or sneezes. Influenza can spread from one person to another beginning about one day before symptoms start through about a week after onset.

Influenza symptoms can include a sudden onset of fever, headache, chills, cough, sore throat, and body aches. In children, vomiting and diarrhea might occur. Although most people are ill for less than a week, some people have complications and may need to be hospitalized.  Symptoms usually appear one to three days after exposure.

You can take three important steps to fight the flu:

1) Get vaccinated.

2) Stop the spread of flu and other germs by covering your mouth and nose with a tissue when coughing or sneezing, washing your hands often to help protect yourself from germs, avoiding touching your eyes, nose or mouth, staying home from work, school, and other activities when you are sick, and avoiding close contact with people who are sick.

3) Use antiviral drugs if your doctor recommends them.

For more information on the flu and on how to protect you and your loved ones go to https://www.vdh.virginia.gov/content/uploads/sites/3/2016/01/Influenza.pdf.


Norovirus is a very contagious virus that causes the “stomach flu,” or vomiting and diarrhea, in people.

Anyone can be infected with norovirus and get sick. Because there are many different strains of norovirus, people who have been sick with norovirus can get it again throughout their lifetime.

The virus is found in the stool and vomit of infected people and can spread easily from person to person. People infected with norovirus are most contagious from the time they first start feeling ill through three days after they feel well again. People sometimes remain contagious for up to a month after they have recovered. People can become infected by eating food or drinking liquids that are contaminated by infected food handlers, touching surfaces or objects contaminated with norovirus and then touching their mouth before hand washing, or having direct contact with another person who is infected and then touching their mouth before hand washing. Therefore, good hand washing is the key to preventing the spread of norovirus.

Symptoms usually include nausea, vomiting and/or diarrhea, and stomach cramping. Sometimes people have a low-grade fever, chills, headache, muscle aches, and a general sense of tiredness.

Norovirus disease usually begins 12-48 hours after exposure, but can appear as early as 10 hours after exposure. The illness is usually brief, with symptoms lasting one to three days.

Norovirus disease can be prevented in a number of ways, including:

  • hand washing after using the restroom, changing diapers, sneezing, coughing, and before and after preparing food;
  • disinfecting contaminated surfaces with household chlorine bleach-based cleaners;
  • washing clothing and linens if they become soiled;
  • washing fruits and vegetables thoroughly before eating;
  • avoiding food or water from sources that may be contaminated;
  • cooking seafood completely.

Persons infected with norovirus should not prepare food while they have symptoms and for at least two days after they recover.

For more information on Norovirus visit https://www.vdh.virginia.gov/epidemiology/epidemiology-fact-sheets/norovirus-disease/ or http://www.cdc.gov/norovirus/index.html.

Watch video here: https://www.youtube.com/watch?v=pmy8x2Lm7rE

Zika Virus

Zika virus infection is a viral disease primarily spread to people through bites of infected mosquitoes, but sexual transmission has also been documented. Mosquitoes become infected by feeding on infected persons. Zika virus is transmitted primarily by Aedes aegypti (Yellow fever mosquito). Aedes albopictus (Asian tiger mosquito) can also spread the virus.

Outbreaks of Zika virus infection have occurred in Africa, Southeast Asia, the Pacific Islands, Central America, South America, the Caribbean and Mexico. For a map, see http://www.cdc.gov/zika/geo/index.html. Because the mosquitoes that spread the virus are found around the world, it is likely that outbreaks will spread to new countries. There has not been any reported mosquito-borne transmission of Zika virus in the continental U.S. For a map of where the mosquitoes that could spread Zika virus are located in the U.S., see http://www.cdc.gov/zika/vector/range.html.

Anyone traveling to an area where Zika virus is found can become infected. Infections have been reported in travelers returning to the U.S. from affected areas. Those who do not travel to affected areas are not currently at risk of becoming infected because local spread by mosquitoes in the continental U.S. has not been reported.

About 80% of people who are infected do not become sick. For the 20% who do become sick, the most common symptoms include fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild and the symptoms typically last several days to a week.

Evidence from case reports and experience from related flavivirus infections indicate that the incubation period for Zika virus disease is likely 3–14 days. This means that symptoms are likely to occur from 3 to 14 days after exposure to Zika virus.

There is no vaccine to prevent Zika virus infection. Infections can be prevented by avoiding mosquito bites. This includes wearing long‐sleeved shirts, long pants and socks, using insect repellent or permethrin‐treated clothing (especially during the daytime when mosquitos are active), using air conditioning or window/door screens to keep mosquitos outside, and eliminating standing water from containers in yards (including bird baths, flower pots, buckets) to stop mosquito breeding.

For more information on Zika virus go to https://www.vdh.virginia.gov/zika/ or http://www.cdc.gov/zika/.