Epidemiology & Interpreting Health Data

Epidemiology forms the foundation of public health. It involves the calculation of qualitative and quantitative data to determine the incidence and prevalence of disease, and is utilised to monitor, control and acknowledge health trends in communities and populations. Ultimately, it allows us the ability to determine if a disease is really problematic for a population, or specific population group, and subsequently indicates the appropriate application of health promotion and education targeted towards preventing the transmission of communicable disease, and the development of chronic non-communicable illnesses.It's intended to not only measure disease, health determinants, and mortality, but also to acknowledge what works, and what doesn't, in working towards achieving positive health outcomes and trends.  

epidemics and pandemics!

The Diseases That Threaten Us

Epidemic

An increase, often sudden, in the number of cases of a disease above what is normally expected for a population in a specific area (CDC, 2012).

Pandemic 

The worldwide spread of a new disease (WHO, 2020).

Epidemics and pandemics are incredibly scary, and that's with good reason when we look at how they've impacted us historically. The 1918 pandemic of H1N1, or Spanish Influenza, is the deadliest pandemic seen in recorded human history. Throughout its path of destruction, the virus instilled fear in global communities as it took the lives of typically healthy adults, causing over 50 million deaths worldwide, totalling 3% of the recorded global population (CDC, 2019). 

"the mother of all pandemics"

The thing with epidemics and pandemics is that they defy the expansive progress and extensive knowledge held within our modern medical and health services. Experts and researchers ponder whether a communicable disease outbreak in the present day could mirror the outcomes seen in the 1918 influenza pandemic, and many believe to a certain extent - despite the advancements in vaccines, medical practice and health promotion - that it's possible due to the pathogens evolving and lurking in the ecosystems of our globalised world - cue, front and centre today - the 2019 Novel Coronavirus (CDC, 2019). 

the 2019 novel coronavirus

A global public health emergency

We've seen strains of the coronavirus before, in both Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS), however the 2019-nCOV is only just emerging. 

Origins

In December 2019, an unprecedented measure of pneumonia cases emerged in Wuhan, Hubei, China. Despite clinical presentations greatly resembling those of viral pneumonia, the cause of the outbreak was initially unknown until a shared history of exposure to the Huanan Seafood Market was identified across the patients. Formal investigation of the outbreak began on 31st December 2019, narrowing in on the source of the developing epidemic and the market closed on 1st January 2020 (CDCC, 2020). The patients were isolated whilst a team of physicians, epidemiologists, virologists, and government officials was formed in the province to commence work on identifying and addressing the disease. "Deep sequencing analysis from lower respiratory tract samples indicated a novel coronavirus" (Huang, et al, 2020).

 

As indicated through the use of the term 'novel', this virus has not previously been identified. However, virological analysis has identified that the n-CoV closely resembles coronavirus present in chrysanthemum bat populations residing in the Chinese province of Yunnan. It is most likely that this is the primary source of the virus, however this is not proven. Lesser known, is the intermediary host infected with the virus prior to its transmission to humans (Huaiyu, 2020). 

 

On 20th January 2020, the virus was classified as a 'Class B Notifiable Disease', enforcing the legal requirement that all diagnosed cases be reported to China's Infectious Disease Information System (CDCC, 2020). The outcome of this is increased reporting, resulting in a subsequent increase in the solidity and reliability of data attained and reported. 

On Thursday 29th January 2020, the World Health Organisation declared the virus a global health emergency, highlighting their concern surrounding the increasing incidence of the virus, and the associated mortality rate, globally, as well as diagnosis in those who have not recently travelled to China (Huang, et al, 2020).

The 2019 novel coronavirus is considered to be less severe than other coronavirus, like SARS, however it is more contagious (CDCC, 2020). Virologists attribute this to a few points:

  1. The virus has the ability to spread during the incubation period (the period between exposure to an infection and the appearance of the first symptoms, which for the novel coronavirus can be up to 14 days) meaning it is contagious for a long time;

  2. The clinical symptoms are atypical, and in some cases present asymptomatically (the absence of symptoms), causing a high possibility of missed diagnosis;

  3. The epidemic coincided with the Chinese Spring Festival, where population movements were frequent enhancing the possibility of viral spread (Huaiyu, 2020). 

...Where are we at now? 

Naming

The World Health Organisation have announced the official name for 2019 n-COV is COVID-19. This is in keeping with the World Health Organisation's guidelines for naming new human infectious diseases. 

Incidence and Epidemic 

As published in the World Health Organisation Situation Report of 20th February 2020, there are 75,748 diagnosed cases globally. Of these 74,675 are in China. 

The reportable diagnostic criteria has changed. Laboratory diagnosis (throat swab) was initially the only method of classifying confirmed diagnosed cases, however diagnosis within the Hubei province has changed to include a clinical diagnosis (assessment by a medical practitioner determined by the presentation of symptoms). This provides us with a better picture of how many people have been infected with the coronavirus. 

 

Given the high incidence of COVID-19 in China, as presented in Table 1, and the low incidence of COVID-19 out of China, as presented in Table 2, the outbreak is considered an epidemic rather than a pandemic.

TABLE 1 - INCIDENCE IN CHINA BY PROVINCE

Situation Report 20 February 2020

World Health Organisation, 2020

TABLE 2 - INCIDENCE OUT OF CHINA BY REGION/COUNTRY

Situation Report 20 February 2020

World Health Organisation, 2020

The Data

The Chinese Centre for Disease Control and Prevention released a publication titled 'The Epidemiological Characteristics of an Outbreak of 2019 Novel Coronavirus Diseases (COVID-19) - China 2020', encompassing a descriptive, exploratory analysis of all novel coronavirus cases diagnosed from 31st December 2019 through 11th February 2020, through utlisation of data taken from China’s Infectious Disease Information System - remember, as of 20th January 2020, all previous and newly diagnosed cases are legally required to be reported here.

This report is in keeping with a cross-sectional study design, which by definition analyses data from a population at a specific point in time. In this instance, we are looking at those diagnosed with COVD-19 in China, since the known onset of the virus. 

The analysis refers to 72,314 diagnosed patients*, however the epidemiological discussion refers only to the 44,672 laboratory confirmed cases.

  • *61% confirmed (laboratory diagnosis), 14.6% clinically diagnosed (Hubei only), and 1.2% asymptomatic (diagnosed based on positive laboratory test result with the absence of symptoms)

The analysis includes:

  1. A summary of patient information;

  2. An examination of age distributions and sex ratios;

  3. Calculating of case fatality and mortality rates;

  4. Geotemporal analysis of viral spread;

  5. Epidemiological curve; and 

  6. Subgroup analysis 

But! we're trying to keep things simple though, so let me break the findings down for you!

Virus Categorisation - COVID-19 has been allocated severity classifications:

  • Mild - category symptoms include non-pneumonia or mild pneumonia

    • ​36,160 confirmed cases** (80.9% of total confirmed cases)

  • Severe - category symptoms include dyspnea (shortness of breath), decreased blood oxygen saturation

    • 6,168 confirmed cases** (13.8% of total confirmed cases)

  • Critical - category symptoms include respiratory failure, septic shock, multiple organ dysfunction/failure

    • 2,087 confirmed cases** (4.7% of total confirmed cases)​​

**Referring to the 44,672 laboratory confirmed cases in China as at 11th February 2020

This shows us that an overwhelming proportion of the diagnosed cases are considered mild, with a smaller proportion developing into severe or critical categorisation dependant on the symptoms present. 

Let's take a deeper look at who's been infected by the virus!

Geographic

  • Hubei Province: 

    • 33,367** confirmed cases (74.7% of total confirmed cases)

    • 979 deaths (95.7% of total attributable deaths)

  • Other (in China):

    • 11,305** confirmed cases (25.3% of total confirmed cases)

    • 44 deaths (4.3% of total attributable deaths)

  • Wuhan related exposure:

    • Yes = 31,974** (85.8% of total confirmed cases)

      • 853 deaths (92.8% of total attributable deaths)

**Referring to the 44,672 laboratory confirmed cases in China as at 11th February 2020

This tells us that the epicentre of the virus, the Hubei Province, is still very much experiencing the brunt of the viral outbreak. It also tells us that of the diagnosed cases in China, a vast majority have exposure to Wuhan - the capital of the Hubei Province, and the home of the Huanan Seafood Market where the initial cases of the virus in humans have been traced back to. 

Age (%**)

  • 0-9 years = 416 (0.9%)

  • 10-19 years = 549 (1.2%)

  • 20-29 years = 3,619 (8.1%)

  • 30-39 years = 7,600 (17.0%)

  • 40-49 years = 8,571 (19.2%)

  • 50-59 years = 10,008 (22.4%)

  • 60-69 years = 8,583 (19.2%)

  • 70-79 years = 3, 918 (8.8%)

  • >80 years = 1,408 (3.2%) 

**Referring to the 44,672 laboratory confirmed cases in China as at 11th February 2020

This tells us that majority of those infected with COVID-19 are in the middle life-span stages. These are typically considered as healthy, low risk age groups, which we'll refer back to when we look at the associated fatality rate.

Fatality Rate 

The fatality rate is the number of deaths from a specific cause. It is calculated by using the following equation:

total number of deaths/total number of confirmed cases x 100

  • Fatality rate for study data set = 2.3% for this data set (11/2/20)

    • Age categorisation:

      • >80 years = 14.8% **

      • 79-79 years = 8.0% **

      • 60-69 years = 3.6%

      • 50-59 years = 1.3%

      • 40-49 years = 0.4%

      • 30-39 years = 0.2%

      • 20-29 years = 0.2%

      • 10-19 years = 0.2%

      • 0-9 years = N/A 

    • Critical viral categorisation fatality rate = 49% 

      • Remember that of the 44,672 confirmed lab diagnosis as at 11th February 2020, 4.7% of total confirmed cases were categorised as critical. 

 

Due to incomplete/missing comorbidity data it is unclear as to whether those diagnosed may be compromised due to specific co-morbid risk factors such as the presence of another disease like cardiovascular disease for example. For the middle life-span age groups, who have the highest incidence of viral infection, the fatality risk if low, compared to the elderly, who are more likely to experience death as an outcome of contracting the virus. A greater understanding of co-morbidity data would allow us to reinforce the hypothesis that those with co-morbid illness, or previously compromised health, are more likely to experience the virus severely or critically than those who are healthy. Nonetheless, this assists us in defining vulnerable population groups by age, which is incredibly helpful in the diagnostic and early treatment stages, as well as promoting literacy towards the virus (what it is, what the symptoms are, what to do, etc.). 

Vulnerable Communities

Anyone exposed to COVID-19 is at risk of contracting the virus, however present epidemiology informs us that most healthy adults host the capacity to recover well. For the elderly, aged 70 or over, the risk of the virus becoming severe or critical is higher than other life-span stages within the population.

The Symptoms 

Through monitoring of the COVID-19 as outlined above, it is now known to present acutely with symptoms resembling 'the flu' or pneumonia, including high body temperature, fatigue, body aches/myalgia, difficulty or laboured breathing, cough, and/or sputum production, and hosts the capacity to develop into a more severe lung infection or acute respiratory distress syndrome (ARDS).

Protecting yourself

The World Health Organisation recommend following the below protocols:

  • Frequently clean hands by using alcohol-based hand rub or soap and water;

  • When coughing and sneezing cover mouth and nose with flexed elbow or tissue – throw tissue away immediately and wash hands;

  • Avoid close contact with anyone who has fever and cough;

  • If you have fever, cough and difficulty breathing seek medical care early and share previous travel history with your health care provider;

  • When visiting live markets in areas currently experiencing cases of novel coronavirus, avoid direct unprotected contact with live animals and surfaces in contact with animals;

  • The consumption of raw or undercooked animal products should be avoided. Raw meat, milk or animal organs should be handled with care, to avoid cross-contamination with uncooked foods, as per good food safety practices.

Learning more!​

The World Health Organisation have developed a course titled "Emerging respiratory viruses, including nCoV: methods for detection, prevention, response and control". You can access it here: https://openwho.org/courses/introduction-to-ncov

positive points

In comparison the the 1918 H1N1 outbreak, we are so far medically advanced that our capacity to address epidemic disease, and potentially subsequent pandemic outbreak is greater than it has ever been before. A glimmer of hope presented itself this week as Australian Researchers at Melbourne's Peter Doherty Institute for Infection and Immunity, advised us they had developed the first lab grown 2019 n-COV reproduction out of China. Today, the virus has been sent to a secure CSIRO research laboratory in Geelong, where the virus will be examined, with the intention of achieving  a 16-week deadline to test a vaccine on humans (Scott & Timms, 2020)

References

CDC. (2012). Epidemic Disease Occurrence. Retrieved 30th January 2020, from: https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section11.html

CDC. (2019). The Deadliest Flu: The Complete Story of the Discovery and Reconstruction of the 1918 Pandemic Virus

. Retrieved 30th January 2020, from: https://www.cdc.gov/flu/pandemic-resources/reconstruction-1918-virus.html#background

Chinese Centre for Disease Control and Protection. (2020). The epidemiological characteristics of an outbreak of 2019 novel coronavirus diseases - china 2020. Retrieved 19th February 2020, from: https://www.ncbi.nlm.nih.gov/pubmed/32064853

Huang, c., Wang, Y., Li, X., Ren, L., Zhao, J., Hu, Y., Zhang, L., Fan, G., Xu, J., Gu, X., Cheng, Z., Yu, T., Xia, J., Wei, Y., Wu, W., Xie, X., Yin, W., Li, H., Liu, M., Xiao, Y., Gao, H., Guo, L., Xie, J., Wang, G., Jiang, R., Gao, Z., Jin, W., Wang, J., Cao, B. (2020). Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. The Lancet. Retrieved 30 January 2020, from https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30183-5/fulltext?fbclid=IwAR2YoQyIszYkDSTs9PM1cFkq6Er6IEK53VATMWlr3vkQZXLLApiVAypLARU#seccestitle180

Huaiyu, T. (2020). 2019-nCOV: New Challenges of Coronavirus. Chinese Journal of Preventative Medicine, 2020, 54(00). Retrieved 20 February 2020, from: http://rs.yiigle.com/yufabiao/1179575.htm

Scott & Timms. (2020). Australian-made coronavirus copy reaches high-security CSIRO laboratory in Geelong. Retrieved 30th January 2020, from: https://www.abc.net.au/news/2020-01-31/australian-made-coronavirus-copy-reaches-high-security-csiro-lab/11915092

 

WHO. (2020). Novel Coronavirus(2019-nCoV) - Situation Report as 20 February 2020. Retrieved 21 February 2020, from: https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200220-sitrep-31-covid-19.pdf?sfvrsn=dfd11d24_2

WHO. (2010). Whats is a pandemic?. Retrieved 30th January 2020, from: https://www.who.int/csr/disease/swineflu/frequently_asked_questions/pandemic/en/

Stephanie Says acknowledges the traditional custodians of the land on which we live - the Wurundjeri people of the Kulin nation. We acknowledge their Elders past, present and emerging. Always was, always will be Aboriginal land. 

Note: Stephanie Sayss is not run by medical professionals. This platform is an educational tool only, and not intended to be used for medical advice. Always seek the assistance of a doctor - this platform is intended to be used a tool to assist you in doing so.

All references are cited on the page they are relevant to. 

©2019 by Stephanie Sayss.