The CDC & Novel Flu Investigations

#14,016

We are rapidly approaching the 10th anniversary of emergence of the 2009 H1N1 swine-origin pandemic virus, and while we often see several decades between pandemics (1918 to 1957, or 1968 to 2009) - as the ECDC graphic above illustrates - sometimes the gaps are considerably shorter.

• 11 years between the 1889 Russian flu and the 1900 Old Hong Kong Flu
• 11 years between the 1957 H2N2 pandemic and the 1968 H3N2 Hong Kong flu
• And just 9 years later -  in 1977 - H1N1 re-emerged after a 20 years absence

As we've discussed previously, we only know the subtypes of influenza that have circulated in humans since early in the last century, but historic accounts suggest at least a dozen `influenza-like’ pandemics occurred in the 400 years prior to the 20th century.

Credit Pandemic Influenza's 500th Anniversary

While some of these dates are a bit fuzzy, there are several instances where pandemics appear to be separated by fewer than 10 years.  Making the notion that we don't have to worry for decades for the next pandemic to emerge clearly erroneous.

And since the 2009 H1N1 virus emerged, we've seen numerous outbreaks (in humans and in non-human species) of novel or variant flu viruses around the world. Most famously, H5N1 in Egypt, and H7N9 in China.

The United States hasn't been immune, and has seen several high profile swine flu outbreaks, and several brushes with novel avian flu viruses, over the past decade.

A few on-topic blogs include:

EID Journal: H3N2v Swine To Human Transmission At Agricultural Fairs – 2012

MMWR: Investigation Into H3N2v Outbreak In Ohio & Michigan - Summer 2016

MMWR: H3N2v Outbreak At Three Fairs — Maryland, 2017

J Infect Dis: Serological Evidence Of H7N2 Infection Among Animal Shelter Workers, NYC 2016

EID Journal: Mammalian Pathogenesis & Transmission of Avian H7N9 Viruses - Tennessee 2017

CDC: IRAT Evaluation Of Novel Avian & Swine Flu Risks

These post-2009 outbreaks have - so far - been contained, or have died out of their own accord.  But just like with an unattended campfire in the woods - it only takes the right conditions for an ember to grow into a wildfire.

The CDC investigates, and takes these novel and variant flu outbreaks seriously.  

Last summer the CDC - in conjunction with the USDA and 4H - released an ambitious 60-page graphic novel on swine variant flu and how disease detectives investigate outbreaks.

The Junior Disease Detectives: Operation Outbreak Graphic Novel

While avian flu appears - at least temporarily - to be on the decline, swine variant influenza remains an ongoing threat.  Last year, 17 confirmed cases were reported in the United States (see CDC chart below), although the true burden is likely much higher.

Credit CDC

The CDC maintains a list (IRAT) with currently 16 (avian, swine & canine) Influenza A viruses they regard as having some pandemic potential (see IRAT: Revisited), that they score by likelihood of emergence and likely impact.

Credit CDC IRAT

Yesterday the CDC published an overview of recent novel and variant flu in the United States, and how they respond to these outbreaks.  I've only included a few excerpts, so follow the link to read it in its entirety.

What CDC Does About Novel Flu: Outbreak Investigations

CDC works with state and local health departments to investigate human outbreaks with novel flu viruses (i.e., flu viruses that do not normally circulate in people) and animal outbreaks caused by unusual or concerning flu viruses in order to:

1. identify the flu virus causing the outbreak,
2. assess the public health risk posed by this virus outbreak,
3. and to help prevent people from getting infected.

CDC takes novel flu outbreaks seriously because of their potential to harm large numbers of people. CDC scientists become concerned when:

• People are infected with animal flu viruses, including swine (pig) and avian (bird) flu viruses, or people are infected with a human flu virus that changed abruptly and significantly, resulting in a new human seasonal influenza A virus (called a novel flu infection in people). Flu viruses are found in animals that are not the usual host for that virus – for example, when avian influenza A(H7N2) viruses were found in cats in a New York City animal shelter;
• Specific influenza viruses of special public health concern are detected– for example, when highly pathogenic avian influenza H5 and H7 viruses are found in U.S. poultry.
  

When any of these scenarios happens, CDC works with state public health officials on a public health investigation and also coordinates with the United States Department of Agriculture (USDA) and state animal health officials as appropriate.

In the case of novel flu, the goals of an outbreak investigation are to identify the source of the infection in people, to determine if person-to-person spread of the virus is happening, and to slow or stop the spread of the virus in people and sometimes animals.

Epidemiologists, sometimes called “disease detectives”, do this type of investigative work. Disease detectives use various methods to figure out the “anatomy of an outbreak.” For influenza, this might include:

• Interviewing people who report illness.
• Asking that all people reporting to a healthcare provider (physicians’ offices, health clinics, hospitals, and other health care facilities) with influenza-like illness (ILI) be evaluated for influenza and that they be reported to the local public health department.
• Interviewing people who have tested positive for flu.
• Evaluating the capacity for person-to-person spread of the virus in question through contact tracing, which is the identification and diagnosis of people who may have come into contact with an infected person.
• Investigating reports of exposure to animals known to carry influenza viruses, such as pigs and birds.
• Monitoring responders to animal influenza outbreaks, such as people working in outbreaks among pigs and poultry.
  

Following are a few examples of this investigative process showing how CDC takes quick action to respond to novel flu outbreaks in order to help stop or slow the spread of disease.

      (Continue . . . )


While seasonal flu season appears to be winding down, and avian flu outbreaks have much declined over the past year or so, the risks of seeing swine-variant flu outbreaks goes up during the summer and fall when county and state fairs are exhibiting pigs.

Add in 500 years of pandemic history, and the fact that most novel and swine flu outbreaks occur with little or no warning, and we have ample reasons to remain alert - and prepared - for when the next viral ember finds the right conditions to become a wildfire.