What is Haemophilus parainfluenzae and why is she a ‘good’ bug?

ZOE runs the largest study of nutrition and gut bacteria in the world, with data from over 10,000 people. We publish our research in top scientific journals, including Nature Medicine. Our scientists have found 15 “good” gut microbes that are associated with indicators of good health and 15 “bad” gut microbes that are linked with worse health. 

Haemophilus parainfluenzae — or “Hannah” as we call her — is one of the 15 “good” bugs. In this article, you can find out more about Hannah, why she is a good bug, and what foods she likes and dislikes. 

Fast facts about your gut microbiome

  • Your gut is home to trillions of bacteria and other microbes that make up your gut microbiome.

  • These microbes mainly feed on fiber and chemicals called polyphenols, which give plants their color, and turn these into chemicals that help support your health and weight control. 

  • Your gut microbiome is unique and radically different from everyone else’s, unlike your DNA, which is 99% the same. Even twins only share 34% of the same microbes. 

  • At ZOE, we use the latest and most advanced biotechnology to analyze the bacteria in your gut from a poop sample.

  • Using this technology, the ZOE program tells you your unique microbiome composition — including which of the 15 “good” and 15 “bad” bugs are in your gut — in order to recommend the best foods for you.

Who is Hannah?

Hannah is part of a group of bacteria called Proteobacteria, one of the largest groups of bacteria. She is generally found in the mouth and upper respiratory tract in most people. 

Hannah can sometimes cause infections, including respiratory tract infections, endocarditis, and arthritis. 

Our scientists found Hannah in the gut of nearly 55% of our study participants.

Why is Hannah a ‘good’ bug?

Until recently, scientists didn’t know much about Hannah aside from her ability to occasionally cause infections. 

Some researchers think that Hannah isn’t a good bug. A recent study indicates that she may promote inflammation in the gut and contribute to a person’s risk of developing inflammatory bowel disease. 

But in our research, we have found links between having Hannah in your gut and having lower insulin secretion and higher insulin sensitivity.

Lower insulin secretion and higher insulin sensitivity are good for your body. Too much insulin is bad for your health, as it increases your risk of obesity, type 2 diabetes, and heart disease. 

ZOE scientists and our world-leading academic collaborators continue to study Hannah to find out more about her and how she contributes to good health. 

What foods does Hannah like and dislike?

Our scientists have found links between specific foods that you eat and the 15 “good” and 15 “bad” gut bugs.

In general, Hannah likes whole grains, legumes, and fruit, particularly apples. She doesn’t like meat, sugary drinks, alcohol, tea, or coffee. 

But the exact foods that will help Hannah thrive in your body depend on the combination of bugs in your gut. Since every person’s gut microbiome is completely unique, there is no one-size-fits-all diet that is right for everyone. 

The ZOE program analyzes your entire microbiome and works out your unique “gut booster” and “gut suppressor” foods, so that good bugs, like Hannah, can flourish.

If you want to know the best foods for your body and your unique combination of gut bugs, take our free quiz today. 


Identification of polysaccharide capsules among extensively drug-resistant genitourinary Haemophilus parainfluenzae isolates. Scientific Reports. (2019).


Immunoglobulin A targets a unique subset of the microbiota in inflammatory bowel disease. Cell Host & Microbe. (2021).


Insulin: Too much of a good thing is bad. BMC Medicine. (2020).


Microbiome connections with host metabolism and habitual diet from 1,098 deeply phenotyped individuals. Nature Medicine. (2021).