Five Things to Remember When Interpreting Epidemiologic Data

Five Things to Remember When Interpreting Epidemiologic Data

1. Data changes over time.

VDH collects data on COVID-19 from a number of different sources. Laboratory, morbidity and case reports, vital statistics (i.e., death certificates), medical and vaccination records, and information collected during case investigations (i.e., patient interviews) are many of the data sources used. Sometimes these sources contain different information. For example, we may get a lab report that does not include the patient’s address. To count this case, we use the address of the patient’s doctor, but later when the local health department performs a COVID-19 case investigation, we may learn of the patient’s home address and update their COVID-19 case record. As a result, the case may be moved to a different county based on the change in address. VDH performs ongoing and comprehensive quality assurance on COVID-19 cases, hospitalizations, and deaths. Every time VDH reports data, we are reporting the most up-to-date information we have at that time. All data are preliminary and subject to change. More information can be found in the Quality Assurance Steps for COVID-19 Data.

2. Data we share underrepresents the true number of COVID-19 cases in Virginia.

The number of COVID-19 cases reported by VDH is likely less than the true burden of COVID-19 in Virginia. Not everyone with COVID-19 develops illness; as a result they may not seek medical treatment and then are not tested. For persons who do get sick, not everyone has access to or will seek medical treatment. Additionally, not everyone who is sick will seek testing to confirm their illness is caused by COVID-19. VDH may never know about these cases.

3. Cases are classified using a standardized case definition.

Public health uses standardized case definitions to determine who is a case and who is not for epidemiological surveillance. Having a case definition makes it possible to compare data trends over time, across counties, and between Virginia and other states. A case definition is different from a diagnosis and is used for a different purpose. A diagnosis is helpful for treatment and medical billing while a case definition is used for public health surveillance to monitor the burden of disease. For COVID-19, Virginia uses the national CDC COVID-19 case definition for counting cases for surveillance. 

Most often, a case is only counted once, even if a person has multiple positive tests.  However, there are instances where a person may be counted as more than one COVID-19 case. This may happen when a person tests positive again after 90 days from the first test, or when a person tests positive for COVID-19 with a different SARS-CoV-2 variant, which could indicate potential re-infection. On September 1, 2021, VDH adopted the Centers for Disease Control and Prevention (CDC) COVID-19 2021 Case Definition. This definition provides criteria for counting a new case of COVID-19 in the same person separately from a case that was already counted in Virginia. Re-infection of COVID-19 is still being analyzed in Virginia.

4. Our surveillance data are intended to answer questions about the epidemiology of COVID-19.

There are different data sources used to summarize the COVID-19 pandemic, and the numbers may be different for things that sound the same. For example, the Virginia Hospital and Healthcare Association has a dashboard with  the number of hospitalizations for people who have tested positive for COVID-19 or who have test results pending. These data help measure the current burden on the healthcare system and prepare hospitals for a possible surge in new cases. These data do not have the same kind of case definition that epidemiologic case data do because they are not intended for the same purpose. VDH reports hospitalizations using COVID-19 case investigations to estimate severity of disease. The hospitalization of a case is captured at the time the local health department performs the case investigation. This underrepresents the number of hospitalizations in Virginia because a person  may become hospitalized after the case investigation. It is important that VDH uses the same case definition to report all COVID-19 cases, including those hospitalized.

5. There are limitations to the data we share.

Public health epidemiologists work hard to make sure data are presented as accurately and timely as possible, but there are limitations to any data source. We have presented some of the surveillance challenges above, but there are many other limitations to our data. VDH has experts in infectious disease epidemiology, community health, data visualization, and public communication working to make the data we share as accurate, useful, and easy to understand as possible.

*Originally posted May 1, 2020

Virginia COVID-19 Response: Meat and Poultry Processing Plants

The number of COVID-19 cases, outbreaks, hospitalizations and deaths associated with meat and poultry processing plants continue to remain very low throughout Virginia. As long as there is community transmission of COVID-19, it is likely that we will continue to see occasional cases in meat and poultry processing plant workers over time.

COVID-19 vaccines are now available that are safe and highly effective at preventing serious illness, hospitalization, and death. Vaccination, combined with other interventions to prevent transmission of the virus that causes COVID-19, such as masking, distancing, frequent hand washing, and staying home when sick or after an exposure, have helped to greatly reduce the rates of COVID-19 observed in this worker population.

With reported cases of COVID-19 cases on the decline and vaccination efforts increasing, the monthly poultry data insights blog is being discontinued. If you have questions about cases of COVID-19 in meat and poultry processing plant workers in your area, please contact your local health department.

For more information about the COVID-19 vaccines, visit vaccinate.virginia.gov or call 877-VAX-IN-VA (877-829-4682).

Virginia COVID-19 Response: Meat and Poultry Processing Plants

This data will be updated at the beginning of each month.

The meat and poultry data blog looks different this month—why the change?

The number of COVID-19 cases, outbreaks, hospitalizations and deaths associated with meat and poultry processing plants continue to remain very low throughout Virginia. As long as there is community transmission of COVID-19, it is likely that we will continue to see occasional cases in meat and poultry processing plant workers over time. The focus of the COVID-19 response efforts for meat and poultry processing plant workers has shifted from supporting outbreak investigations to providing vaccine access to this essential workforce.

What efforts have been made to improve COVID-19 vaccine access to meat and poultry processing workers?

VDH and the food sector have been working on various ways to distribute COVID-19 vaccines to meat and poultry processing workers. These include working with occupational health providers and local health departments. In addition to these efforts community-based organizations have been working to share information about COVID-19 vaccines with workers in the food and agriculture sector.

  • The Lord Fairfax Health District (LFHD) has been working with local food processors to set up vaccination clinics. They’ve vaccinated local fruit growers and a few food processing plants and are continuing to reach out to businesses to arrange coming on site to get more people vaccinated. Since January 2021, LFHD has vaccinated at least:
    • 405 meat and poultry processing plant workers
    • 255 dairy workers
    • 170 produce workers
    • 130 other food production workers
    • 43 migrant workers
  • The Central Shenandoah Health District (CSHD) scheduled 15 clinics onsite at poultry plant facilities, administering over 2,770 1st and 2nd COVID-19 vaccine doses. The health district utilized Community Health Workers to work with poultry plant workers and their families to get connected to other clinics if they were unable to or uncomfortable with receiving the vaccine at the onsite clinics at their place of employment. These efforts supported the districts’ larger, weekly clinics at the Rockingham County Fairgrounds and James Madison University where essential workers, including poultry plant workers, food processing, and agricultural workers, were invited to come and receive a COVID-19 vaccine. Furthermore, CSHD engaged with poultry plant facilities to establish COVID-19 vaccine programs within their occupational health programs. So far, this effort has resulted in the establishment of one COVID-19 vaccine program at a local poultry plant.
  • The Eastern Shore Health District (ESHD) has:
    • Been offering COVID-19 vaccinations to seasonal workers as they arrive on the Shore and coordinating that effort with local farm managers and crew leaders.  Out of approximately 130 workers currently on the Shore, it is estimated that  80-85% have been vaccinated; some received the vaccine before they arrived.
    • Partnered with Eastern Shore Rural Health to provide three onsite vaccination events at poultry plant facilities. Hispanic and Haitian Creole outreach workers helped provide education to workers as part of these events. A total of 91 night shift workers were vaccinated during these events and similar events are planned for day shift workers in early June. The Elite Marketing Group will be helping to host a pre-vaccination “party” with snacks and educational information as part of these upcoming events.
    • Offered weekly walk-in vaccination clinics on Tuesdays and Wednesdays at the local health department.
    • Partnered with Legal Aid and Eastern Shore Rural Health to plan an upcoming outdoor event at the local YMCA, to specifically offer COVID-19 vaccines to the refugee, immigrant and migrant populations. There will be informational tables for organizations who provide services to this community and walk-up vaccine opportunities for anyone 12+ with all three authorized vaccines available to maximize vaccine uptake.
    • Hired one Hispanic and one Haitian Creole Community Health Worker who will be working primarily with poultry, agricultural, aquaculture and seasonal workers, which comprise a large part of the refugee, immigrant and migrant community.
Why is COVID-19 vaccination so important?

COVID-19 vaccination is an important tool to help us get back to normal; every vaccine administered helps us get closer to reaching population immunity. Population immunity means that enough people in a community are protected from getting a disease because they’ve already had the disease or because they’ve been vaccinated. Population immunity makes it hard for the disease to spread from person to person. It even protects those who cannot be vaccinated, like newborns or people who are allergic to the vaccine. Learn more about the benefits of getting vaccinated.

Why the focus on meat and poultry processing workers?

Initial cases of COVID-19 associated with meat and poultry processing plants were reported in Virginia in March of 2020. Cases peaked in April and May of 2020 with large outbreaks reported in several processing plants throughout the United States, including Virginia. Workers in these facilities need to work closely to one another, often for prolonged periods of time, making transmission of COVID-19 from one worker to another easy. Protecting this vulnerable workforce is important to protect both the workers, who produce the food we eat, and the communities in which they live.

In addition to vaccination, what other interventions were put in place to prevent the transmission of disease within these facilities and the wider communities in which they exist?

The Virginia Department of Health worked with affected facilities to put a variety of interventions in place to reduce disease transmission. The most common interventions implemented in Virginia included:

  • educating employees about the transmission of COVID-19
  • screening employees for signs and symptoms of illness
  • adding hand hygiene stations
  • adding physical barriers between workers where physical distancing was not possible, and
  • requiring universal face coverings

For more information about recommended interventions for meat and poultry processing facilities, check out the links below:

Enhanced Public Reporting of COVID-19 Outbreaks

What is now included that was not reported before?
Beginning on May 7, 2021, the Virginia Department of Health (VDH) will publicly report outbreaks with laboratory evidence from any diagnostic test meeting the COVID-19 outbreak definition. Previously, VDH only publicly reported COVID-19 outbreaks with laboratory confirmed cases from molecular amplification tests (MATs), like PCR tests. Now, VDH will report COVID-19 outbreaks with cases identified by any diagnostic test, such as antigen tests, to more accurately represent the burden of COVID-19 outbreaks.

Why?
COVID-19 cases associated with an outbreak are often underreported. This is because not everyone seeks testing or are identified as part of an outbreak during the public health investigation by VDH staff. However, the impact on a community is the same regardless of whether an outbreak consists of cases with positive PCR or antigen tests. In an effort to inform the community about what is occurring in their area, it is important to share all COVID-19 outbreaks that are being investigated.

Why now?
As testing and reporting of COVID-19 cases have evolved, so has VDH’s approach to outbreak reporting. Early in the pandemic, only people with a positive PCR test were classified as a COVID-19 case. However, later, when antigen tests received Emergency Use Authorization  from the United States Federal Drug Administration (FDA), people with positive antigen tests  were counted as probable cases of COVID-19. Many healthcare facilities and school-based testing programs use only antigen testing options. Reporting outbreaks with positive lab results from antigen or PCR tests more accurately informs the public about how many COVID-19 outbreaks there are in their community.

Will VDH include outbreak data since the beginning of the pandemic?
No, outbreak data will be updated retrospectively from January, 1, 2021. VDH conducted an evaluation of COVID-19 outbreak data and methods for public reporting. Analysis of COVID-19 outbreak data shows an increase in reported outbreaks with antigen only lab tests beginning January 1, 2021. VDH is prioritizing outbreak data for 2021 to share relevant and actionable data to the public now.

COVID-19 Outbreaks Associated with Meat and Poultry Processing Plants in Virginia

This data will be updated at the beginning of each month.

What is a COVID-19 outbreak?

An outbreak is an increase in the number of cases of disease observed. In Virginia, an outbreak of COVID-19 is defined as two (2) or more lab-confirmed cases associated with a facility.

How many outbreaks have occurred in meat and poultry processing facilities in Virginia?

To date, a total of 17 COVID-19 outbreaks in meat and poultry processing facilities in Virginia have been identified.

How many confirmed cases of COVID-19 have been associated with these outbreaks? How many people experienced serious illness resulting in hospitalization or death?

The total number of confirmed cases, hospitalizations and deaths associated with these outbreaks is shown in the tables below.

Confirmed Cases1 Hospitalizations1,2 Deaths1
1368 54 9

 

Confirmed Cases by Region1
Central 61
Eastern 810
Northern 0
Northwestern 497
Southwest 0
TOTAL 1368

How have the outbreaks associated with meat and poultry processing facilities changed over time?

Initial cases of COVID-19 associated with meat and poultry processing plants were reported in March of 2020. Cases peaked in April and May. Facilities implemented multiple interventions to reduce and prevent viral transmission. Cases have since decreased significantly and only sporadic cases are being reported at this time.

Chart by Visualizer
What interventions were put in place to prevent the transmission of disease within these facilities and the wider communities in which they exist?

The Virginia Department of Health worked with affected facilities to put a variety of interventions in place to reduce disease transmission. The most common interventions implemented in Virginia included:

  • educating employees about the transmission of COVID-19
  • screening employees for signs and symptoms of illness
  • adding hand hygiene stations
  • adding physical barriers between workers where physical distancing was not possible, and
  • requiring universal face coverings

For more information about recommended interventions for meat and poultry processing facilities, check out the links below:

Might more cases be seen in these facilities over time?

As long as there continues to be increased community transmission of COVID-19, it is likely that we will continue to see occasional cases in meat and poultry processing plant workers over time.

Footnotes:

For more information about epidemiologic data shared by the Virginia Department of Health, check out our Five Things to Remember When Interpreting Epidemiologic Data.1 All data is preliminary and subject to change over time.

2 Hospitalization status at time case was investigated by VDH. This underrepresents the total number of hospitalizations in Virginia.

Source: Cases – Virginia Electronic Disease Surveillance System (VEDSS)