Thursday, May 9, 2013

New emerging strain of H7N9


Avian Influenza A (H7N9)


Avian Influenza A (H7N9) is a subgroup of influenza viruses that normally circulate among birds. There are many strains of H7N9. Despite the fact that this virus does not normally infect human, human infection with H7N9 continues to be reported in China. To date, there are a total of 131 confirmed cases of avian influenza A (H7N9) in China (8 May 2013). There are 32 fatalities, 55 patients are hospitalized and 44 patients have been discharged.  Eight provinces in China are affected (Anhui, Fujian, Henan, Hunan, Jiangsu, Jiangxi, Shandong and Zhejiang).


Case definition:

Confirmed Case: A patient with novel influenza A (H7N9) virus infection that is confirmed by CDC’s Influenza Laboratory or a CDC certified public health laboratory using methods agreed upon by CDC and CSTE.1

Probable Case: A patient with illness compatible with influenza for whom laboratory diagnostic testing is positive for influenza A, negative for H1, negative for H1pdm09, and negative for H3 by real-time reverse transcriptase polymerase chain reaction (RT-PCR), and therefore unsubtypeable.

Case Under Investigation: A patient with illness compatible with influenza meeting either of the following exposure criteria and for whom laboratory confirmation is not known or pending, or for whom test results do not provide a sufficient level of detail to confirm novel influenza A virus infection.

   A patient who has had recent contact (within ≤ 10 days of illness onset) with a confirmed or probable case of infection with novel influenza A (H7N9) virus.
OR

   A patient who has had recent travel (within ≤ 10 days of illness onset) to a country where human cases of novel influenza A (H7N9) virus have recently been detected or where novel influenza A (H7N9) viruses are known to be circulating in animals.

Transmission:

At the moment, there is no person-person transmission reported but many people infected with H7N9 are reported to have contact with poultry. People can get infected when they touch an infected bird or contaminated environment and then touch their eyes, nose or mouth. Virus can be found in huge amount in birds’ dropping and mucus.

Symptoms:

Symptoms include fever, cough and shortness of breath. The disease may progress to severe pneumonia, acute respiratory distress syndrome, septic shock, multi-organ failure and death.

Diagnostic tool:

Currently, the only test available to detect H7N9 is real-time Reverse Transcriptase Polymerase Chain Reaction (rRT-PCT). Samples from respiratory tract (eg: nose, throat, lung) are taken and brought to public health lab. The results typically ready within 4 hours.

Treatment:

Basically, there was no early data available for the early use of neuraminidase inhibitor in those who are infected with H7N9. Lab testing with functional assay indicates that H7N9 is susceptible with neuraminidase inhibitor but resistant to adamantanes (eg: amantadine, rimantadine).  The clinical benefit is greatest when it is administered early (within 48 hours) but the drug must be given as soon as possible for those who are indicated even though the onset of disease has been more than 48 hours.  

The group of people who are indicated for the use of neuraminidase inhibitor:

a.     Confirmed case
b.     Probable case
c.      H7N9 cases under investigation.

Patients who are at high risk for developing complication when contracting H7N9:

a.     Age less than 2 years old or ≥ 65 years old.
b.     Patient younger than 19 years old who is on long-term aspirin medication.
c.      Alaska natives or American Indians.
d.     Patient with underlying medical conditions.
e.     Pregnant women or postpartum (within two weeks after delivery) women.
f.      Immunosuppressed patients – under immunosuppressed drug or HIV.
g.     Morbidly obese (BMI≥40)
h.     Resident of nursing home or other chronic care facilities. 

The duration of neuraminidase inhibitor:

5 days but can be extended in severely ill patients and immunosuppressed patients.




Special precaution:

a.     Age ≥ 65 years old: No dosage reduction is required if age alone is considered.
b.     Pregnancy: The dose is similar to non-pregnant women. Pregnancy category C medication. Zanamivir is more preferable than oseltamivir due to its limited systemic absorption.
c.      Impaired renal function: No dose adjustment is recommended by manufacturer for inhaled zanamivir. Oseltamivir dose should be reduced if creatinine clearance is 10-30 ml per minute. The dose should be reduce of 75 mg twice daily to 75 mg once daily.

Vaccine:

There is no vaccine available at the moment.

References:
1.  Avian Influenza A H7N9. Centers for Disease Control and Prevention.   
     (http://www.cdc.gov/flu/avianflu/h7n9-virus.htm)(accessed 9 May 2013)
2.  Avian Influenza A(H7N9). Ministry of Health Malaysia. 
     (http://www.moh.gov.my/press_releases/401)(accessed 9 May 2013)

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