Which diseases have generated the highest number of cases from Outbreaks during the first two decades of the 21st century?  In this blog, we can use GIDEON’s data to find out.

‘Disease outbreak’ is a scary term for many, but every year we suffer dozens, if not hundreds, of localized and international disease outbreaks across the world. While these outbreaks are always significant to those affected, they rarely generate headlines,  and can sometimes go unnoticed outside of the Healthcare Industry.

An “outbreak” is often defined as an increase in case numbers for a particular disease in a defined place and time. Outbreaks can evolve into pandemics (such as with COVID-19) or consist of an isolated cluster of cases, especially for rare and less-communicable diseases, and can persist for years and even decades.

GIDEON collects information on all cases of Infectious Disease worldwide, and much of this effort involves gathering data on outbreaks. The following list has been created using these data, assessing all outbreaks in excess of 500 cases reported from January 2001 to November 2020 – from the GIDEON database of 361 diseases and 233 countries and territories.

10. Hand, foot & mouth disease (Enterovirus infection) – 2.9+ million outbreak cases

Prominent in Asia, especially over the last 10 years, the most significant outbreaks occurred in 2016 and 2017 – accounting for over 2 million out of total cases. The disease typically affects children, causing a distinctive rash, fever, and nausea (not to be confused with foot-and-mouth disease, which generally only affects livestock).

9. Viral Conjunctivitis – 4.3+ million outbreak cases

Many outbreaks of this disease were recorded across Asia and South America, the most significant of which was in South Korea in 2002. The latter outbreak resulted in more than 1 million cases. Brazil has also suffered repeated outbreaks, with 10,000 to 100,000 cases reported throughout this period. Often linked with upper respiratory diseases, viral conjunctivitis is also referred to as a ‘pink eye’ due to its principal symptom.

8. Measles – 5.4+ million outbreak cases

Surprisingly, measles has been one of the most common causes of outbreaks into the 21st century, involving much of the world.  The most notable of these outbreaks occurred in 2019, with nearly 1.5 million cases reported across 50 countries. The disease is best known for its distinctive combination of fever, cough, and a florid rash.

7. Viral Meningitis – 5.4+ million outbreak cases

While the bacterial variant of the disease is typically associated with large outbreaks in sub-Saharan Africa (a region known as the ‘meningitis belt’), viral meningitis outbreaks are far more common.  Unusually large outbreaks have been reported in China, often affecting neighboring countries as well. Over 4.5 million cases were reported in the region between 2008 and 2012.  Viral meningitis is associated with a stiff neck, headaches, and high fever. Fortunately, rates of fatal viral meningitis have been steadily decreasing for a number of years.

6. Chikungunya – 9.7+ million outbreak cases

Sometimes mistaken for Dengue or Zika, Chikungunya was most active in the Americas region in recent years.  Even the United States has reported local transmission, which South American countries have experienced hundreds of thousands of Chikungunya cases. Joint pain, high fever, and a rash are the characteristic symptoms, with headaches, chronic pain, and insomnia appearing in later stages of the disease.

5. Viral Gastroenteritis – 10.2+ million outbreak cases

This entry is a bit of an anomaly here since the vast majority of cases were associated with a single outbreak. In 2006, viral gastroenteritis in Japan was caused by Norovirus, with no less than 10 million cases, – impacting the entire country. Symptoms include diarrhea and/or vomiting, accompanied by abdominal cramps and fever.

4. Cholera – 12.8+ million outbreak cases

Cholera is an ancient disease that continues to produce regular and significant outbreaks, with case numbers in the 100,000s almost every year. A recent large outbreak that began in 2016 in Yemen, continues to this date – already totaling more than 2.4 million cases. The disease causes severe diarrhea and vomiting, resulting in extreme loss of fluids that can turn a patient’s skin to a bluish-gray color – as they succumb to dehydration. 

3. Dengue – 26.0+ million outbreak cases

The number of Dengue outbreaks has been increasing in recent years, with cases reaching almost 5 million in 2019 alone. Brazil has experienced major difficulties with this disease, as have neighboring countries, and much of Asia and Africa. Dengue is characterized by high fever, vomiting, headaches, musculoskeletal pain, and a characteristic rash. 

2. Malaria – 27.7+ million outbreak cases

This mosquito-borne disease typically causes fever, headache, fatigue, and vomiting, but can be complicated by seizures, coma, multi-organ failure, and death in severe cases. Malaria outbreaks have been somewhat less frequent than other diseases on our list over the  21st century; however, the severity and impact of malaria outbreaks are relatively high.  Two major outbreaks of over 8 million cases each have occurred during the past four years. This is not to downplay the overall burden of disease, which the World Health Organization estimated to be as high as 229 million cases in 2019 alone.

1. COVID-19 – 64.5+ million outbreak cases (at the time of writing)

A disease which did not even exist until eleven months ago – is at the top of our list.  The growing number of cases and deaths have made “COVID-19” the most commonly used word used by mankind.  The disease can have a wide range of symptoms but commonly causes coughing, fever, loss of smell and taste, and breathing difficulty. Elderly individuals and those with pre-existing conditions are particularly at risk of developing complications. Even with a vaccine available in the next few months, we must all remain cautious and follow safety measures at all times. 

Stay healthy, stay safe!

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