data = StringIO(
    """
Date     Week Number   Influenza[it]  Febbre[it]  Rinorrea[it]  
2008-01-01             1            220         585           103   
2008-01-08             2            403         915           147   
2008-01-15             3            366         895           136   
2008-01-22             4            305         825           136   
2008-01-29             5            311         837           121
"""
    )
df = pd.read_csv(data, sep='\\s{2,}', parse_dates=['Date'], engine='python')
Convert a common date format in an ISO week date format