With several studies published May 9 and 10, a clearer picture has emerged of how influenza A(H7N9) propels many of its victims toward death. It’s a nasty way to go, but sometimes mercifully swift, for a malady that kills around one in four of those who contract it.
On March 31, 2013, public health specialists in China reported the first three cases of human infection with influenza A(H7N9) to the World Health Organization. Since then, many of the confirmed H7N9 patients have been hospitalized, had severe to critical illness, and died.
Governments around the world and the scientific and medical communities have moved quickly to assess the power of the new avian flu strain and determine ways of combating it. On Friday, China upgraded its instructions to local health organizations and WHO published a new risk assessment. Here’s the story thus far about how this unfamiliar disease claims lives.
Chickens spread much of new H7N9 flu
Influenza A(H7N9) appeared in humans for the first time early this year in the nation of China. So far, over half the cases have been linked to exposure to fowl, especially chickens. Oddly, the new flu is not associated with poultry farms, but with the “wet markets” where vendors offer live fowl. Many of these markets in eastern China have suspended operations or closed since the flu outbreak began. Swine have not been implicated.
First flu symptoms appear after a week
The new H7N9 avian virus, found only in China and Taiwan (one case in a traveler) so far, kicks in with symptoms of influenza-like illness after about seven days following exposure. Fatigue, fever, and dry cough set in. Headache and muscle and joint pain may also occur. The disease can remain invisible to polymerase chain reaction tests on throat swabs for up to a week. Most symptomatic patients are male (71%) and over 60 years old. Also, about three-quarters have at least one underlying health condition. These additional risk factors include hypertension, other lung conditions, diabetes, and heart disease, in that order.
Worsening symptoms lead to hospitalization
High fever, increased sweating and fatigue, cough, nasal congestion, and/or difficulty breathing usually lead to the patient’s initial health care visit. Antipyretics and expectorants may be used to reduce symptoms. Natural and synthetic traditional Chinese medicines have been applied orally or by injection throughout the course of the disease. Treatment with oseltamivir (Tamiflu) or or zanamivir is recommended as soon as possible with suspected or confirmed cases. It can reduce the possibility of death even if given up to 5 days after onset of illness. This flu resists adamantane and rimantadine.
Hospitalization within a day (8 days after initial infection) of influenza A(H7N9) has been routine. Protocol in Chinese hospitals has involved prompt isolation, active monitoring of the patient’s close contacts, and standard, contact, and droplet precautions by staff.
Pneumonia develops and may become severe
This type of influenza progresses rapidly. In the next several days, the patient’s lungs become inflamed as the system continues to fight the virus. Lower respiratory disease ensues. Fluid begins to fill the alveoli and impair exchange of oxygen and carbon dioxide.
Chest X-rays reveal signs of pneumonia. In patients whose disease progresses, severe pneumonia develops within 5-7 days of the initial symptoms.
Sophisticated devices render pulmonary assistance.
As it progresses, pneumonia may require measures to assist breathing. These can range from administering supplemental oxygen by mask, nasal prongs, or intubation, to mechanical ventilation. Blood oxygen levels sink and carbon dioxide builds up, poisoning the blood through acidosis.
Sepsis begins to cascade.
The cascade of sepsis begins with a sudden system-wide inflammatory response to infection. Some antibiotics are administered immediately, and specific antibiotics can be used after diagnostic tests. The patient receives large amounts of intravenous fluids and drugs such as dopamine or norepinephrine. Heart rate increases. Blood pressure drops as the patient goes into septic shock.
Pneumonia and/or sepsis cause acute respiratory distress syndrome
As pneumonia and sepsis proceed, an H7N9 patient may suddenly enter acute respiratory distress syndrome. Radiographs vary strikingly from normal. Shortness of breath worsens, the patient becomes confused, alveolar damage occurs throughout the lungs, and not enough oxygen can reach the bloodstream. Caregivers must begin mechanical ventilation at this point, and deep sedation may become necessary. ARDS is about 90% fatal if untreated, 50% if treated with mechanical ventilation in a hospital intensive care unit.
Multiple organs begin to fail
Septic shock causes multiple organ dysfunction syndrome as the body’s continued inflammatory response to the H7N9 virus injures other organs. (Cigarette smoking and heavy alcohol use aggravate the problem.) Intensive care personnel must use mechanical ventilation, hemodialysis, inotropic or vasopressor agents, and parenteral nutrition to sustain life. Lungs, brain, liver, kidneys, and other major organs fail, including heart. Septic shock kills around half of those who suffer it.
Death results from either ARDS or MODS.
As of May 10, the WHO has reported 131 confirmed H7N9 cases. These include 32 deaths, making the early mortality rate about one in four. The discharge rate so far appears to be somewhat lower. Through a late April report published in JAMA, median duration from the onset of illness to death among confirmed and fatal cases was 11 days. More mild cases have been discovered as research has progressed through April and early May.