Oseltamivir Treatment Produces Small Reduction in Secondary Influenza Illness

By Will Boggs MD

NEW YORK (Reuters Health) - Treatment of influenza with oseltamivir brings a small reduction in the spread of influenza to household members in a crowded, low-income setting, according to a study in Bangladesh.

"In this study the index patient (first one ill in the household) received oseltamivir treatment -- no one else," lead author Dr. Alicia M. Fry from Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, told Reuters Health. "The decrease in secondary household illness is consistent with a decrease in infectiousness of the oseltamivir-treated patient. This is consistent with the decrease in virus shedding."

Neuraminidase inhibitors like oseltamivir have been shown to prevent influenza infection when given before or immediately after exposure to an infectious person, but studies supporting a reduction in secondary transmission after primary treatment are scarce.

As part of an oseltamivir efficacy trial in Dhaka, Bangladesh, Dr. Fry and her colleagues collected respiratory specimens for influenza from nearly 4,700 household members of 1,190 index patients.

The researchers found lower rates of secondary influenza when the index patient had received oseltamivir rather than a placebo (8% vs. 10%, p=0.031), they report in Lancet Infectious Diseases, online March 16.

In contrast, the rate of PCR-confirmed secondary influenza did not differ significantly between the oseltamivir and placebo groups (4% vs. 4%, p=0.319), although only few household members gave a specimen for analysis.

The significant benefit of oseltamivir treatment appeared to be limited to households in which index treatment started 48 hours or more after illness onset.

"Because it is not 100% effective at stopping virus shedding, patients who receive oseltamivir for treatment should continue to use appropriate infection control measures until symptoms resolve," Dr. Fry said. "If prevention of infection is the primary goal, then chemoprophylaxis of susceptible persons should be considered."

She added that "if oseltamivir was used for treatment in the setting of a pandemic or seasonal epidemic, in addition to the effects on decreasing symptoms and reducing complications, one would expect a modest decrease in infectiousness and in secondary household illnesses -- sort of an extra perk."

"Even a slight reduction in household transmission, in the setting of widespread use of antiviral treatment during a community influenza epidemic or pandemic, might result in reductions in overall disease burden," the researchers conclude. "Our findings offer additional evidence of the potential public health benefit of antiviral influenza treatment."

The research was funded by the CDC.

"Oseltamivir/zanamivir and other anti-influenza drugs should be reserved for the use of very severe cases of influenza and for those people that are known to have more severe effects if they do become infected with influenza (e.g., pregnant women/obese people and those with chronic lung/heart conditions)," said Dr. Ian G. Barr from the WHO Collaborating Centre for Reference and Research on Influenza at Peter Doherty Institute for Infection & Immunity in Melbourne, Australia.

"I am not sure it should be used at all in this setting unless it was a very severe pandemic that had not already spread into the community," Dr. Barr, who co-wrote a commentary on the report, told Reuters Health by email. "To really stop or even slow an influenza epidemic or pandemic, one would need to treat all index cases and contacts, which is extremely difficult (and expensive to do) especially in a place like the crowded regions of Dhaka."

"We do need new classes of influenza antiviral drugs," Dr. Barr concluded. "The neuraminidase inhibitors (like oseltamivir and zanamivir) are not wonder drugs and have only a moderate effect on treating and preventing influenza in most settings."

SOURCE: https://bit.ly/1BMgBqo and https://bit.ly/1ImuQHo

Lancet Infect Dis 2015.

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