H1N1 influenza, or the swine flu, is a novel influenza virus. The virus circulates during the year, with increased prevalence during the winter months. It is transmitted from person to person via airborne droplets from coughs or sneezes. But contrary to other influenza viruses, the H1N1 influenza virus affects children and young adults in higher numbers than older people.
General
Most patients with H1N1 feel tired with general malaise. They also have body aches and feel muscle weakness. Fever is a common finding, and it can lead to chills. The H1N1 virus tends to also cause vomiting and diarrhea, which can lead to dehydration and affect the renal function, leading to electrolyte imbalance. Among the electrolytes affected are sodium and potassium. Too high or too low sodium can lead to seizures. High potassium can lead to dangerous cardiac arrhythmias. Another common symptom of H1N1 influenza is myositis, or inflammation of muscles. The breakdown product of myositis, myoglobin, can lead to rhabdomyolysis, in which the myoglobin clogs the kidneys tubules, leading to renal failure.
Respiratory
Like other influenza viruses, the H1N1 virus' most prominent symptoms are respiratory symptoms. Patients with H1N1 have runny, congested noses; dry, repetitive coughs; respiratory distress with rapid breathing, and retractions (pulling in of abdominal and chest muscles as the patient tries to pull in oxygen-rich air). Some patients become hypoxic, in which the oxygen content in the blood drops to dangerous levels. Other respiratory symptoms of H1N1 include sore throat, difficulty swallowing and stridor, a high-pitched noise on inspiration that resembles the noise made during choking. The H1N1 influenza virus can predispose the patient to bacterial infections, most notably with streptococcal pneumonia. Patients with pneumonia have worsening respiratory symptoms and need for supplemental oxygen, which can lead to respiratory failure and the need for intubation and mechanical ventilation.
Neurological
H1N1 influenza infection can produce encephalitis. This is an inflammation of the brain, which presents with altered mental status (confusion, irritability, loss of consciousness, memory loss), fever, headache, photophobia (fear of bright lights) and neck stiffness, which mimics the symptoms of meningitis. The other neurological symptom of H1N1 influenza infection is seizures. These are triggered by fever or by the inflammation the virus causes in the brain and surrounding tissues.
