Haemophilus influenzae is a Gram-negative bacterium most often linked to respiratory and invasive infections, but it can also exist in the human gut microbiome. While less common in the gut than in the respiratory tract, it can persist there without causing illness, particularly in people with a healthy and diverse microbiome. However, disruptions such as antibiotic use can allow it to multiply, increasing the risk of gut inflammation or enabling it to move to other parts of the body where it may cause infection (Figueira et al., 2023; Servaas, 2022; Mao et al., 2023).

In South Africa, H. influenzae remains clinically relevant, mainly because of its role in community and hospital-acquired infections, though gut colonisation is rarely tested outside research settings. Monitoring gut levels could help identify people at risk for opportunistic infections — especially those with weakened immunity or an imbalanced gut microbiome — and support preventative health strategies.

✔ Type: Gram-negative bacterium, often found in the respiratory tract but can also be present in the gut.

✔ Role in the Gut: Usually not a dominant gut resident, but can be part of the microbiome in low numbers without causing illness.

✔ Opportunistic Pathogen: Can cause infections when the immune system is weakened or gut balance is disrupted, especially after antibiotic use.

✔ Spread: Mainly through respiratory droplets; gut colonisation may occur via ingestion of contaminated material.

✔ Disease Risk: Invasive strains can cause pneumonia, meningitis, and bloodstream infections; in the gut, overgrowth may trigger inflammation or infection elsewhere.

✔ Prevention: Maintaining a healthy gut microbiome and avoiding unnecessary antibiotic use can reduce risks.

✔ Relevance to South Africa: Remains a public health concern due to its role in both community-acquired and hospital-acquired infections.

While Haemophilus influenzae (H. influenzae) is mainly known for its role in respiratory infections, small, balanced amounts in the gut may contribute to microbial diversity. In healthy individuals, it can coexist with other bacteria without causing harm, potentially playing a role in competitive exclusion, where harmless bacteria occupy space and resources, making it harder for harmful pathogens to take over (Servaas, 2022; Wang et al., 2023).

This balance can support overall gut health by maintaining ecosystem stability. However, its protective potential depends entirely on keeping levels low and in check. When the microbiome is diverse and resilient — supported by diet, probiotics, and avoiding unnecessary antibiotics — opportunistic bacteria like H. influenzae are less likely to cause disease. They may help maintain a healthy microbial community.

When Haemophilus influenzae (H. influenzae) levels become too high in the gut, it can increase the risk of opportunistic infections. This overgrowth may allow the bacteria to move beyond the gut and cause illness, especially in people with weakened immune systems or disrupted microbiomes (Servaas, 2022; Wang et al., 2023).

Common signs and potential consequences include:

✔ Diarrhoea or other digestive upset

✔ Abdominal discomfort or cramps

✔ Signs of systemic inflammation (e.g., body aches, chills)

✔ Fever and fatigue if the infection spreads beyond the gut

✔ Respiratory symptoms such as cough or difficulty breathing

✔ Serious illnesses like meningitis or bloodstream infections in severe cases

Such outcomes are more likely after antibiotic use that disrupts the healthy gut balance, creating an opportunity for H. influenzae to overgrow.

In South Africa, Haemophilus influenzae (H. influenzae) is primarily known as a respiratory pathogen, but emerging evidence shows it can also be part of the gut microbiome. In healthy individuals, it may be present in low numbers without causing harm. However, when the gut microbiome is disrupted — for example, after antibiotic use — H. influenzae can overgrow and increase the risk of opportunistic infections (Servaas, 2022; Wang et al., 2023). These infections may spread beyond the gut, potentially leading to conditions like bacteraemia, meningitis, and respiratory illness.

The risk is higher among vulnerable groups such as children, the elderly, and people with weakened immune systems. In South Africa, where antibiotic misuse and high burdens of infectious disease are ongoing public health challenges, this opportunistic behaviour poses a notable concern. Maintaining a balanced gut microbiome through diet, probiotic support, and cautious antibiotic use can help reduce the chance of H. influenzae overgrowth, protecting both gut and overall health.

Support a Balanced Gut Microbiome: Eat a varied diet rich in fibre (whole grains, fruits, vegetables, legumes) to feed beneficial gut bacteria, which can naturally keep H. influenzae at healthy levels.

Avoid Unnecessary Antibiotics: Antibiotics can wipe out protective gut bacteria, giving H. influenzae the chance to overgrow. Only take them when prescribed and follow your doctor’s guidance.

Include Probiotics and Prebiotics: Probiotics from yoghurt, kefir, or supplements, and prebiotics from foods like garlic, onions, and bananas, can help restore gut balance after illness or antibiotic use.

Strengthen Your Immune System: A strong immune system helps control potentially harmful bacteria. Prioritise regular exercise, good sleep, stress management, and nutrient-rich foods.

Stay Hydrated: Proper hydration supports healthy digestion and helps maintain a balanced gut environment.

Monitor Gut Health When at Risk: If you have a chronic illness, weakened immunity, or frequent gut problems, testing your microbiome (such as through Epicentre’s gut health testing) can help identify any imbalances early.