Nav: Home

Hospital study finds substantial proportion of patients and healthcare workers shed flu virus before symptoms appear

April 15, 2019

New research examining influenza transmission in a tertiary hospital finds that a substantial proportion of patients and healthcare works shed the flu virus before the appearance of clinical symptoms. The findings, being presented at this year's European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Amsterdam, Netherlands (13-16 April), raise the possibility that current influenza infection control measures may not be enough to protect healthcare workers and patients during routine care in hospitals.

The discovery came after Swiss researchers tracked almost 700 healthcare workers and inpatients over two consecutive influenza seasons at the University Hospital in Zurich. They uncovered several transmission clusters that were undetected by routine surveillance.

These results are consistent with previous research which suggests influenza may be spread to others by just breathing, and that coughing or sneezing are not required for transmission [1].

Knowing whether people are infectious in the absence of symptoms is a major concern for infection control in hospitals. While hospital acquired infection from asymptomatic individuals may occur, no prospective studies have investigated the transmission of influenza in the absence of symptoms in acute care.

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

The team tracked flu infection through nasal swabs collected daily, and performed diagnostic multiplex real-time PCR and RNA sequencing on specimens. Contacts between participants were traced, and participants were asked to completed daily diaries of any illnesses.

During the study, 16 (11%) healthcare workers and 19 (4%) inpatients tested were diagnosed with an influenza infection. Most of these 35 participants experienced influenza symptoms, particularly respiratory symptoms, when their tests were positive. However, several remained asymptomatic despite testing positive for influenza infection (2/16; 13% healthcare workers and 2/19; 11% inpatients).

Importantly, 17% (12/71) of influenza-positive swabs from healthcare workers and 8% (3/38) from patients were collected on days that they did not report flu symptoms.

Furthermore, among symptomatic individuals, 14% (2/14) of healthcare workers (but none of the 17 symptomatic inpatients) had a positive influenza test before symptoms developed.

Further analyses based on local and temporal proximity of healthcare workers and inpatients revealed at least seven clusters of potential transmission events among healthcare workers, among inpatients, or between healthcare workers and inpatients. However, evidence based on local and temporal proximity for one possible transmission from an asymptomatic healthcare worker to an inpatient was not supported by genetic analysis.

"Our findings suggest that influenza infection in acute care is common and a significant proportion of individuals appear to shed influenza virus without harbouring any symptoms, making the spread of flu very difficult to control even with self-diagnoses and current infection control practices", says Dr Kuster. "Influenza vaccination is not perfect but remains the best tool we have to protect healthcare workers and their patients from severe illness."

The authors note that more research on how influenza is transmitted in hospitals is needed before it can be firmly established whether people with no clinical symptoms may be contributing to the spread of the virus without realising.

The authors note several limitations including that the study was conducted in a single institution, and the total number of influenza events was moderate. They also note that because participating wards were alerted to the influenza problem, they may have paid more attention to prevention measures, and it is possible that transmission rates may generally be higher than seen in the study.
-end-


European Society of Clinical Microbiology and Infectious Diseases

Related Influenza Articles:

Birds become immune to influenza
An influenza infection in birds gives a good protection against other subtypes of the virus, like a natural vaccination, according to a new study.
Researchers shed new light on influenza detection
Notre Dame Researchers have discovered a way to make influenza visible to the naked eye, by engineering dye molecules to target a specific enzyme of the virus.
Maternal vaccination again influenza associated with protection for infants
How long does the protection from a mother's immunization against influenza during pregnancy last for infants after they are born?
Influenza in the tropics shows variable seasonality
Whilst countries in the tropics and subtropics exhibit diverse patterns of seasonal flu activity, they can be grouped into eight geographical zones to optimise vaccine formulation and delivery timing, according to a study published April 27, 2016 in the open-access journal PLOS ONE.
Influenza viruses can hide from the immune system
Influenza is able to mask itself, so that the virus is not initially detected by our immune system.
Using 'big data' to combat influenza
Team of scientists from the Icahn School of Medicine at Mount Sinai and Sanford Burnham Prebys Medical Discovery Institute among those who combined large genomic and proteomic datasets to identify novel host targets to treat flu.
Rapidly assessing the next influenza pandemic
Influenza pandemics are potentially the most serious natural catastrophes that affect the human population.
Early detection of highly pathogenic influenza viruses
Lack of appropriate drugs and vaccines during the influenza A virus pandemic in 2009, the recent Ebola epidemic in West Africa, as well as the ongoing Middle Eastern Respiratory Syndrome-Coronavirus outbreak demonstrates that the world is only insufficiently prepared for global attacks of emerging infectious diseases and that the handling of such threats remains a great challenge.
Study maps travel of H7 influenza genes
In a new bioinformatics analysis of the H7N9 influenza virus that has recently infected humans in China, researchers trace the separate phylogenetic histories of the virus's genes, giving a frightening new picture of viruses where the genes are traveling independently in the environment, across large geographic distances and between species, to form 'a new constellation of genes -- a new disease, based not only on H7, but other strains of influenza.'
Influenza A potentiates pneumococcal co-infection: New details emerge
Influenza infection can enhance the ability of the bacterium Streptococcus pneumoniae to cause ear and throat infections, according to research published ahead of print in the journal Infection and Immunity.

Related Influenza Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#532 A Class Conversation
This week we take a look at the sociology of class. What factors create and impact class? How do we try and study it? How does class play out differently in different countries like the US and the UK? How does it impact the political system? We talk with Daniel Laurison, Assistant Professor of Sociology at Swarthmore College and coauthor of the book "The Class Ceiling: Why it Pays to be Privileged", about class and its impacts on people and our systems.