Croup is an upper airway infection commonly found in young children. Heart disease includes a wide range of conditions involving the heart and blood vessels. In some  cases, there is a connection between croup and heart disease. Unfortunately, research directly linking both these conditions is low, but it is worth exploring. 

Overview of croup

Definition and causes of croup 

Croup is one of the most common respiratory diseases found in children, particularly those under 5 years old. Croup is typically caused by a viral infection named parainfluenza virus, although it can also be caused by a bacterial infection.¹

Factors causing croup

• Virus: parainfluenza virus, influenza A and B, measles, adenovirus and respiratory syncytial virus (RSV).¹
• Bacteria: Bacterial Croup is divided by the position of infection¹
  • Laryngeal diphtheria is caused by Corynebacterium diphtheriae. This bacterial infection usually begins with a viral infection followed by a bacterial infection, which causes worsened illness¹
  • The common bacterial causes are Staphylococcus aureus, Streptococcus pneumoniae, Hemophilus influenzae, and Moraxella catarrhalis¹

Symptoms and typical progression of croup 

Symptoms:¹ 

• Inspiratory stridor
• Seal-like barking cough 
• Fever

These symptoms can cause difficulty breathing, and may become worse at night. Sometimes fever and difficulty breathing develop due to an infection. Breathing and heart rate may increase from normal. Nasal flaring, retraction, and rarely cyanosis (blue skin discolouration due to abnormalities in blood circulation) can be observed visually. Normally the disease will last for 3 to 7 days with the most severe symptoms on days 3 or 4.¹

Common treatment and management strategies

The treatment and management of croup depends on its severity, it usually consists of:

• Corticosteroids are the key treatment of all patients with croup because they can help faster resolve the symptoms, decrease the return rate to medical care, and reduce the time to stay in hospital.² 
• Epinephrine.
• Oxygen to help resolve agitation.
• Antibiotics

In general, croup is considered a viral infection, so the use of antibiotics will not be encouraged. Antibiotics are usually used to treat primary and secondary bacterial infections. Vancomycin and cefotaxime are reserved for use in severe cases of bacterial infection or secondary bacterial infection.

Overview of heart disease

Definition and types of heart disease

Heart disease, or cardiovascular disease, are illnesses involving the heart and blood vessels. Heart diseases consist of coronary artery disease (CAD), cerebrovascular disease (CVD), peripheral artery disease (PAD), and aortic atherosclerosis.³

Heart disease may result from emboli which clog blood vessels, especially small blood vessels, restricting blood supply to that area. Factors of heart disease occur because of different reasons. For example, emboli in atrial fibrillation leading to ischemic stroke and rheumatic fever, are one of the main factors related to atherosclerosis, which is a common cause of heart disease.⁴ Atherosclerosis results from various factors such as abnormal lipid levels, inflammation and endothelial dysfunction.

Risk factors and common symptoms

Various factors are associated with an increased risk of heart disease. 

Common risk factors of heart disease:⁵

• Smoking
• Diabetes
• Hypertension
• Dyslipidaemia
• Obesity
• Family history

Moreover, low-income status and less education, which are related to other risk factors,  are also strongly associated with heart disease.⁴

Overview of prevention and treatment options

For prevention and treatment, lifestyle modifications are recommended for all heart disease patients; this can include changing diets, increasing exercise, weight control, reducing alcohol, and quitting smoking.⁶ 

Moreover, since lack of exercise is a key risk factor for heart disease, it is recommended that people should do moderate intensity cardio exercise for at least 150 minutes per week, or at least 75 minutes of vigorous exercise and weight training at least 2 days per week.⁷ 

In diet control, a diet should contain more fruits, vegetables, fish, whole grains, and fiber, whilst taking into consideration the necessary calorie intake.⁷ 

For drug treatment, medicines will be prescribed depending on patients’ symptoms. Some drugs can reduce chest pain and manage medical conditions such as lowering lipid profile or blood pressure. Some medicines will help improve other underlying diseases such as high blood sugar, and obesity.⁸ 

• Medicines controlling blood pressure: calcium channel blockers⁸ 
• Medicines reducing blood pressure and reducing heart’s burden: ACE inhibitors and beta blockers⁸ 
• Preventing or relieving chest pain: Nitrate⁸ 
• Medicines reducing the levels of lipids: Statins, Ezetimibe, PCSK9 inhibitors, fibrate or omega-3 fatty acids supplements⁸ 
• Medicines for blood sugar control such as metformin, empagliflozin⁸ 
• Medicine to control weight such as liraglutide, semaglutide or orlistat⁸ 

Possible Connections Between Croup and Heart Disease

One of the risk factors for heart disease is inflammation from infection. Infections including viruses, bacteria, fungi, or toxic substances, can cause inflammation of the heart muscle or inflammatory cardiomyopathy (myocarditis), which is mostly involved in viral infection.⁹ In poor prognosis, this illness usually comes together with left ventricular dysfunction (the abnormal function of the lower left heart chamber), heart failure, or arrhythmia (the abnormality of the rate or rhythm of the heartbeat.¹⁰

The association between croup and heart disease remains unclear, but there are some interesting points and correlations to consider. As mentioned above, croup is associated with airway infection by viruses and bacteria resulting in inflammation, and some links between these types of viruses and the bacteria in croup and myocarditis partially share the same species. Hence, it potentially reflects a relationship between croup and heart disease.

The link between viral infection and heart disease

Viruses found in both myocarditis and croup are adenovirus, influenza A and B virus.

Influenza A and B viruses

These influenza viruses use signalling proteins that control inflammation in the body to induce a toxic process in the heart, or trigger an autoimmune response to fight substances in the heart. Symptoms can vary depending on the amount and area of the heart muscle involvement and presentation timing.¹¹ Common symptoms finding the infection starts involving heart disease are chest pain, heart failure symptoms and arrhythmias. Many studies show that one influenza virus strain is related to the release of pro-inflammatory substances in the human immune and innate immune response.¹¹ However, this inflammation appears to be rare, with younger female patients exhibiting a tendency to develop severe lung symptoms¹¹.

Adenovirus

Adenoviruses are a group of viruses that can infect the airway and cause common cold or flu-like symptoms.¹² These can also lead to acute inflammation of the heart muscle (acute myocarditis) and inflammatory cardiomyopathy.⁹ These viral infections can lead to heart muscle injuries.⁹

The link between bacterial infection and heart disease

Streptococcus pyogenes

Streptococcus pyogenes causes an infection known as group A streptococcus. This viral infection can cause rheumatic heart disease, because of the damage to heart valves from abnormal immune response.¹³ After approximately 3 weeks, this infection causes fevers (or acute rheumatic fever), and affects the heart to induce abnormal immune function to injured heart valves. Moreover, this can lead to inflammation in the heart muscle or rheumatic carditis.¹³ 

Staphylococcus aureus

Staphylococcus aureus infection can lead to endocarditis, which is a life-threatening disease. Endocarditis is an infection of the inner layer of the heart or associated with the heart valves. This is commonly found in the elderly population, or people who have previously undergone surgery, such as valve replacement surgery.¹⁴ These bacteria can enter the body in many ways, including through infection, needles, or tubes, and they enter the blood and go to the heart.¹⁴

Corynebacterium diphtheriae

Corynebacterium diphtheriae produces toxins that can cause diphtheria. Its toxin can spread to the heart, nervous system, and kidneys; which can lead to myocarditis, one of the serious complications of diphtheria.¹⁵ Diphtheria is a serious illness which can become life-threatening. Currently, it remains  rare  in the UK, because there is a vaccine that can prevent it.¹⁶

Case report combination of croup and heart disease

Although no study explains the direct connection between croup and heart disease,  some cases of croup and myocarditis exist. A case study of a 3-year-old girl that developed croup for 5 days, with severe respiratory problems and was admitted because of respiratory failure. After intubation, acute myocarditis was observed and confirmed that she got infected by Corynobacterium diphtheriae. Additionally, similar cases have been reported of the connection between acute croup and myocarditis.¹⁷ However, developing croup related to diphtheria infection and myocarditis depends on areas which are mostly found in developing countries and rarely found nowadays due to preventive vaccines.

Impact of inflammation from croup on cardiovascular health

The potential connection between croup and cardiovascular disease, particularly myocarditis, could be infections that inflame  the heart muscle. In addition, some viruses or bacteria can induce abnormal functions of autoimmune response to injure heart muscle. There is not enough evidence to support that croup can cause heart disease. Croup is commonly not a severe illness and it is self-recovery. Only patients with severe airway symptoms will tend to develop heart disease.

Preventive measures and lifestyle considerations

Tips for preventing croup

In general, croup is found in children. You can help prevent the contact or spread of croup in your family by:

• Washing your hands regularly and correctly¹⁸
• Remind your children to wash their hands before eating or touching their mouths¹⁸ 
• If someone has croup, stop sharing cups and other dishware, avoid direct contact and stay at home to reduce spread¹⁸
• Ensure the child is vaccinated¹⁹ 

When to see the doctor?

If a child’s condition worsens or has severe symptoms of croup,  the parent should go to see the doctor if any of the following symptoms are observed:¹⁹ 

• Difficult to breathe
• Pale or bluish skin
• Severe cough spells
• Difficulty swallowing
• Difficulty taking a breath
• A whistling sound with breath or high-pitched breathing while sitting or resting
• Excessive drowsiness

Summary

Croup is an infection of the upper airways that results in difficulty breathing, a seal’s bark cough, and swelling around vocal cords. It is common in children. The cause of croup is commonly viral infection, but bacterial infection also results in illness. One of the risk factors for heart disease is infection. This leads to the link between croup and the potential for heart disease; however, more studies are needed to support this connection. To my knowledge, only severe croup symptoms or untreated croup can develop heart disease. Therefore, if someone has a possibility of severe croup, he or she should contact their GP.

FAQ

What happens if croup is left untreated?

Croup commonly has mild symptoms, but it can be dangerous if there is an infection in the tissue that covers the trachea (windpipe) or epiglottis, leading to the swollen trachea and shutting of the airway. If this airway blockage is not treated properly, patients can have severe difficulty breathing or stop breathing.¹⁹