Hospital study reveals that a significant proportion of patients and health workers eliminate the influenza virus before the onset of symptoms

A new study on influenza transmission in a tertiary hospital revealed that a significant proportion of patients and health care professionals shed the influenza virus before the onset of clinical symptoms. The findings, presented this year at the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) in Amsterdam, the Netherlands (April 13-16), suggest that current measures of infection control by the Influenza may not be sufficient to protect health care workers and patients during pregnancy. routine care in hospitals.

This discovery took place after Swiss researchers had followed nearly 700 health care workers and hospital patients in two consecutive influenza seasons at the University Hospital Zurich. They discovered several transmission groups that were not detected by routine surveillance.

These findings are consistent with previous research that suggested that flu could be transmitted to other people simply by breathing and that there was no need to cough or sneeze for transmission. .

Knowing if a person is contagious in the absence of symptoms is a major concern for infection control in hospitals. Although asymptomatic infections may occur in the hospital, no prospective study has been conducted on influenza transmission in the absence of symptoms in acute care.

To provide more evidence, Dr. Stefan Kuster of the University Hospital and the University of Zurich in Switzerland and his colleagues conducted a prospective study of influenza virus transmission trajectories in 542 patients in medical services and 152 acute care health care workers working in the same departments during 2015 / Influenza seasons 2016 and 2016/2017.

The team monitored influenza infection with nasal swabs collected daily and performed multiplex sequencing and real-time diagnostic PCR on samples. Contacts between participants were traced, and participants were asked to fill in daily diaries of all diseases.

During the study, an influenza infection was diagnosed in 16 (11%) health care workers and 19 (4%) inpatients. Most of these 35 participants had flu-like symptoms, including respiratory symptoms, when their tests were positive. However, several patients remained asymptomatic despite positive tests for influenza infection (2/16, 13% of health care workers and 2/19, 11% of hospitalized patients).

Importantly, 17% (12/71) of influenza swabs positive for HCWs and 8% (3/38) of patients were collected on days when they did not report flu-like symptoms.

In addition, among symptomatic individuals, 14% (out of 14) of the health professionals (but none of the 17 symptomatic hospitalized patients) had a positive influenza test prior to the onset of symptoms.

Additional badyzes based on the local and temporal proximity of health care workers and hospitalized patients revealed at least seven clusters of potential transmission events among health care workers, among hospitalized patients or between health care workers. health and hospitalized patients. However, evidence based on the local and temporal proximity of a possible transmission of an asymptomatic health worker to an inpatient patient was not supported by genetic badysis.

"Our findings suggest that influenza infection in acute care is common and that a significant proportion of individuals seem to transmit the influenza virus without presenting symptoms, which makes the spread of influenza is very difficult to control even with self-diagnosis and current infection control practices, "said Dr. Kuster. "Influenza vaccination is not perfect but remains the best tool we have to protect health care workers and their patients from serious diseases."

The authors note that it is necessary to conduct more research on the mode of transmission of influenza in hospitals before it can be established with certainty whether people with no clinical symptoms can contribute to the spread of the virus without s & # 39; To give an account of it.

The authors note several limitations, including the fact that the study was conducted in one facility and that the total number of influenza events was moderate. They also note that since the participating rooms have been made aware of the problem of influenza, they may have paid more attention to prevention measures and it is possible that transmission rates are generally higher than those observed in the study. .

Provided by
European Society of Clinical Microbiology and Infectious Diseases