Allison Erickson Descriptive Epidemiology Project: Norovirus

1. Define the problem (nature, extent, significance, etc.)

The problem of the norovirus is that it is highly contagious and does not affect more people over others. When an individual is infected with norovirus, the intestines become inflamed. This inflammation causes abdominal pain, nausea, diarrhea, and vomiting. A significant part of the norovirus is that it can infect many people at one time, due to it being highly contagious. According to Baylor College of Medicine (BCM) (2012), “Noroviruses are thought to be responsible for close to 90% of epidemic, non-bacterial outbreaks of gastroenteritis around the world. In the United States alone, noroviruses are estimated to cause 21 million illnesses each year and contribute to some 70,000 hospitalizations and 800 deaths.”

In addition, the problem with the norovirus is that it can cause large economic problems and overwhelm public health facilities. When the norovirus enters a public health facility, an elder home, or school, it can spread rapidly. Once the norovirus enters a public facility, like those listed, it is extremely difficult for the virus to be contained. Continuing, the norovirus is difficult to diagnose, therefore making it difficult to contain.

2. Describe the Agent

Norovirus are the most common causes of gastroenteritis in the United States (BCM, 2012). This type of infection can be caused by numerous agents such as contaminated foods (uncooked fruits, vegetables, and shellfish), contaminated drinking water, or even direct contact with an individual infected with norovirus. Closed institutional settings are the main areas where norovirus is contracted. These institutional settings include daycare, schools, nursing homes, cruise ships, and college dormitories. When someone is infected with norovirus, the main mode of transmission to another person, food, or surface is through the stool or vomit (BCM, 2012).

Pathologically, noroviruses are in a virus family known as the Calicivirus family. “Caliciviruses are single-stranded, positive-sense RNA viruses” (BCM, 2012). These Caliciviruses are difficult to study because they have an inability to grow in a cell culture system. The Norwalk virus was the first of the noroviruses identified as the causative agent behind an outbreak of gastroenteritis (BCM, 2012). See picture one.

3. Describe the condition (briefly)

The “stomach flu” and “food poisoning” are terms used for norovirus description (CDC, 2012). In error, however, chemicals and germs can also cause food poisoning. Common symptoms of norovirus are diarrhea, vomiting, nausea, and stomach pain. In addition, individuals suffering from norovirus may experience fever, body aches, and headache (CDC, 2012). Symptoms of diarrhea and vomiting can occur

Allison Erickson Descriptive Epidemiology Project: Norovirus

numerous times per day, lasting up to three days, on average. When the symptoms are severe enough, dehydration is another symptom. Dehydration can be dangerous especially in children, older adults, and those with preexisting illnesses.

Getting infected with norovirus can happen numerous times in one’s life because there are many types of noroviruses. This virus is found in stool even before an individual feels sick and can stay in the stool for two weeks or longer after feeling better. Someone is most contagious when sick with norovirus and during the first three days after recovery. Infection of norovirus can occur from numerous vehicles. These vehicles include, eating food or drink handled by someone with norovirus, touching surfaces or objects that have come in contact with the virus, and having direct contact with someone infected with norovirus.

4. Examine the above sources for data on morbidity and mortality in the selected health problem.

In the United States, alone, norovirus causes about 20 million cases of gastroenteritis each year (CDC, 2013). Within that same number, it is estimated that one in every 15 Americans will get norovirus every year. There are over 70,000 hospitalizations and 800 deaths each year in the United States caused by norovirus. During 2009-2010, out of 1,527 foodborne disease outbreaks, norovirus accounted for 42 percent of the outbreaks (CDC, 2013).

According to Koo, Ajami, Atmar, and DuPont (2010), “noroviruses are the leading cause of foodborne disease outbreaks worldwide, and may soon eclipse rotaviruses as the most common cause of sever pediatric gastroenteritis, as the use of rotavirus vaccines becomes more widespread.” Approximately 900,000 cases of pediatric gastroenteritis are caused by norovirus in industrialized nations. In addition, about 1.1 million cases and 218,000 deaths are the result of norovirus in developing nations (Koo et al., 2010).

5. Summarize these data on the distribution of the selected health problem according to the following factors, using tables, graphs, or other illustrations whenever possible.A. Host Characteristics

1. Age: Norovirus can infect anyone, no matter the age. However, older adults are more

susceptible to becoming infected due to low immunity and high outbreak numbers in assisted living or long-term care facilities. Please see figure one.

Allison Erickson Descriptive Epidemiology Project: Norovirus

2. SexAccording to the CDC (2012), in 2009-2010, 71 percent of those that were

infected were females and 29 percent were males. Please see figure two.

3. NativityThe name “norovirus” originated after an outbreak of viral gastroenteritis in a

school in Norwalk, Ohio in 1968. This is why norovirus is sometimes referred to as “Norwalk” virus. Norovirus is actually a strain of a large number of different strains of gastroenteritis, but it continues to evolve (Royal Society for Public Health (RSPH), n.d.). In more detail, in October 1968, the CDC investigated an outbreak of acute gastroenteritis at an elementary school in Norwalk, Ohio. In a matter of two days, 50 percent of the students and faculty developed the illness. Stool samples were collected from volunteers and after subsequent tests of the organisms, researchers concluded that the norovirus was the etiologic agent (Conly & Johnston, 2003).

4. Marital Status There is no scientific or epidemiological evidence that norovirus infects a

married individual more than a non-married individual.

5. Ethnic GroupNorovirus is not more present in certain ethnic populations over another.

B. Environmental Attributes 1. Geographic areas

In 2009-2010 43 reporting sites in the United States and territories reported at least one outbreak of person-to-person gastroenteritis. Across all reporting sites, the median outbreak incidence was 4.7 per million per year (CDC, 2012). Please see Figure three and table four.

2. Social and economic factorsa. Income

All low, medium, and high income households are at risk for becoming infected with norovirus. In lower income communities, sanitation may not be a top priority. Therefore, with a lack of cleaning hands, foods, and surfaces, norovirus can be transmitted easily. Middle income communities are at similar risks because any norovirus on hands or a surface can be transmitted. In addition, schools and daycare facilities are prime locations for norovirus to spread quickly. High income communities may have higher sanitation standards, but norovirus can still be transmitted from person-to-person. With a high rate of norovirus in nursing homes and assisted living

Allison Erickson Descriptive Epidemiology Project: Norovirus

facilities, one can make the inference that middle or higher income individuals can afford living in these facilities.

b. HousingIn 2010-2011, long-term care facilities saw the highest number of norovirus

infection. Another location that has seen an increase in norovirus outbreaks is on cruise ships. Cruise ship norovirus outbreak was responsible for four percent of the outbreaks in 2010-2011. Please see figure five.

3. OccupationBecause norovirus infection is high in long-term care facilities, daycares, and

schools, the people who work in these environments are at risk for being infected. Even in public places like shopping malls, grocery stores, and exercise facilities, any employee who comes in contact with a surface or person with norovirus can become infected.

4. EducationThere is no data suggesting a correlation between norovirus and education

level.

C. Temporal Variation

1. Secular There is little information about secular trends of norovirus. Because norovirus

can mutate and change quickly, accurately diagnosing it can be difficult. Therefore, the only information found was for recent years. Please see cyclic variation.

2. CyclicAccording to 2001-2009 data from the CDC (2012), norovirus outbreak was

highest in 2006-2007. 3. Seasonal

Most outbreaks of norovirus occur in the winter months. An estimated 83 percent of norovirus outbreaks on 2009-2010 occurred between October and March (CDC, 2012). Please see figure seven. Similarly, epidemiological surveillance in England and Wales in 1992-2000 showed that norovirus outbreaks were most frequent during the winter months (CDC, 2010). Please see figure eight.

4. Epidemic

Allison Erickson Descriptive Epidemiology Project: Norovirus

There is little to no information about point epidemics of norovirus. This can be attributed to a lack of communication about the start of an outbreak, the number of cases, and how long the virus lasted.

D. Any additional characteristic that contributes to an epidemiologic description of the disease.

The only additional information to add is that norovirus is continually mutating, therefore it is difficult to gather descriptive information about the disease in a timely and effective manner. In addition, many cases of norovirus go unreported because it is likely termed “stomach flu” or “food poisoning.” Most of the descriptive epidemiological information about norovirus is from the last 20 years. Also, there is limited information about norovirus outbreak in developing countries, which limits some of the descriptive epidemiology from a worldwide stance.

6. Summarize any current hypotheses that have been proposed to explain the observed distribution.

Frequency of norovirus is most likely inconsistent with actual outbreaks due to lack of reporting. However, from the observed distributions, person-to-person transmission is an important cause of norovirus outbreak in the United States. In 2009-2010, there is a possibility of bias in results from the observed distributions due to lack of reporting age of the person infected. Continuing, in some cases, employees of workplaces saw a lower number of norovirus attack rates, which can be attributed to better hand hygiene practices, immunity from frequent exposure to pathogens, and reluctance to report illness (CDC, 2012). Unlike enteric bacterial illnesses (like shigella), which like to peak in summer months, norovirus peaks during the winter months, but can it can still present itself during summer. In all, norovirus is a virus that does see more prevalence in facilities that have high person-to-person transmission risk. Because norovirus is highly contagious, anyone is at risk for getting it, no matter the season, location, or food eaten.

7. List the principal gaps in knowledge about the distribution of the health problem- Underreporting is a problem for analysis of the distribution of norovirus. As stated

prior, many people mistake the norovirus as the “stomach flu” or “food poisoning.” This mistake leads to individuals not seeking medical treatment where the numbers would be reported, as well as not communicating with source of the outbreak (facility, person, etc.).

- Reporting from particular countries is not consistent, leaving room for error in outbreak cases of norovirus.

Allison Erickson Descriptive Epidemiology Project: Norovirus

- When reporting norovirus outbreaks via the National Outbreak Reporting System (NORS), only four variables need to be reported (outbreak identification, date of first illness, reporting site, and total ill). Although that information makes reporting a little easier for sites reporting an outbreak, it does result in various levels of completeness where other variables could be reported like age, gender, setting, and etiology.

- A need to define the duration of the infectiousness of food handlers and to have clarity about the role of asymptomatic food handlers in regards to norovirus.

- Few evidence-based interventions exist for preventing and controlling foodborne illness outbreak of norovirus (CDC, 2012).

8. Suggest areas for further epidemiologic research. Areas for further epidemiologic research should focus on socioeconomic status of

norovirus outbreak. If there is any evidence-based research that would suggest a trend in socioeconomic status and norovirus, that would allow for more focused interventions. In addition, the worldwide data about norovirus outbreak is rather difficult to find. Having a clear reporting system through the World Health Organization would allow health officials around the world to understand and report norovirus appropriately. Further research about person-to-person outbreaks would provide a better understanding of the virus pathogens and how they can be spread. In addition, continuing the monitoring of cruise ships for sanitation, public health practices, and norovirus outbreaks will help identify the source of outbreak, which may lead to knowledge about norovirus outbreak in other vessels.

Allison Erickson Descriptive Epidemiology Project: Norovirus

Figures, Graphs, and Charts

Picture 1:

X-ray structure of the Norwalk virus capsid, with the inset showing details of the structure of the subunits.The different colors represent different regions of the capsid protein.Courtesy: Dr. B.V.V. Prasad (BCM, 2012)

Figure 1:

Percentage of cases in outbreaks of acute gastroenteritis transmitted by person-to-person contact, by age group distribution and etiology — National Outbreak Reporting System, United States, 2009–2010 (CDC, 2012)

Allison Erickson Descriptive Epidemiology Project: Norovirus

Figure 2:  

Percentage of cases in outbreaks of acute gastroenteritis transmitted by person-to-person contact, by sex and etiology — National Outbreak Reporting System , United States, 2009–2010 (CDC, 2012)

Figure 3:

Rate of outbreaks of acute gastroenteritis transmitted by person-to-person contact, by state — National Outbreak Reporting System, United States, 2009–2010 (CDC, 2012)

Allison Erickson Descriptive Epidemiology Project: Norovirus

Table 4: (CDC, 2007)

Figure 5:

Allison Erickson Descriptive Epidemiology Project: Norovirus

Figure 6: Number of reported foodborne norovirus outbreaks by month of first illness onset, United States, 2001–2008. Outbreaks are confirmed as caused by norovirus if fecal or vomitus specimens from >2 persons are positive for the virus by reverse transcription PCR, electron microscopy, or enzyme immunoassay (CDC, 2012)

Figure 7: Number* of outbreaks of acute gastroenteritis transmitted by person-to-person contact, by month of first illness onset and etiology — National Outbreak Reporting System, United States, 2009–2010 (CDC, 2012)

Allison Erickson Descriptive Epidemiology Project: Norovirus

Figure 8: Seasonality of all outbreaks and confirmed Norovirus outbreaks, England and Wales, 1992–2000 (CDC, 2010)

References

Baylor College of Medicine., (2012). Norovirus. Retrieved from: https://www.bcm.edu/molvir/norovirus

Centers for Disease Control and Prevention., (2012). Epidemiology of foodborne norovirus outbreaks, United States, 2001-2008. Retrieved from: http://wwwnc.cdc.gov/eid/article/18/10/12-0833-f2.htm

Centers for Disease Control and Prevention., (2007). Morbidity and mortality weekly report: Norovirus activity – United States, 2006-2007. Retrieved from: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5633a2.htm

Centers for Disease Control and Prevention., (2013). Morbidity and mortality weekly report: Surveillance for foodborne disease outbreaks – United States, 2009-2010. Retrieved from: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6203a1.htm?s_cid=mm6203a1_w#tab1

Allison Erickson Descriptive Epidemiology Project: Norovirus

Centers for Disease Control and Prevention., (2012). Norovirus: Overview. Retrieved from: http://www.cdc.gov/norovirus/about/overview.html

Centers for Disease Control and Prevention., (2012). Outbreaks of acute gastroenteritis transmitted by person-to-person contact – United States, 2009-2010. Retrieved from: http://www.cdc.gov/mmwr/preview/mmwrhtml/ss6109a1.htm

Centers for Disease Control and Prevention., (2010). Two epidemiological patterns of norovirus outbreaks: Surveillance in England and Wales, 1992-2000. Retrieved from: http://wwwnc.cdc.gov/eid/article/9/1/02-0175-f1.htm

Centers for Disease Control and Prevention., (2012). Vessel sanitation program: About the vessel sanitation. Retrieved from: http://www.cdc.gov/nceh/vsp/desc/aboutvsp.htm

Conly, J.M., & Johnston, B.L., (2003). Norwalk virus – Off and running.

Koo, H.L., Ajami, N., Atmar, R.L., & DuPont, H.L., (2010). Noroviruses: The principal cause of foodborne disease worldwide. Discov Med, 10(50), 61-70. Retrieved from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3150746/

Royal Society for Public Health., (n.d.) Norovirus: Preventing the spread of infection.