Sqlite database remains open and File locked after using statment

I've an issue with some sqlite code, it seems that something in the function below is causing the database to remain open after it ought to have been closed by the using statement, I can work round the issue with a call to GC.collect() in the calling function, but I'd like to try and work out the cause of the issue. I've tried adding a call to GC.Collect() after the using statment but this doesn't seem to be enough, asm assuming that something is blocking the GC from clearing up?

    /// <summary>
    /// Gets the Points of Interest for a given Category
    /// </summary>
    /// <param name="rootPath">Target Path</param>
    /// <param name="category">Category to search</param>
    /// <returns>A collection of Points of interest</returns>
    public static Collection<PointOfInterest> GetPointsOfInterest(string rootPath, PointOfInterestCategory category)
    {
        if (category == null)
        {
            throw new ArgumentNullException("category");
        }

        Collection<PointOfInterest> pointsOfInterest = new Collection<PointOfInterest>();

        string databaseLocation = string.Format(Resources.DataFilePath, rootPath, "poidata.db");
        using (SQLiteConnection connection = new SQLiteConnection(string.Format("Data Source={0};Version=3;", databaseLocation)))
        {
            connection.Open();
            using (SQLiteCommand command = new SQLiteCommand(
                "SELECT latmin + (latmax - latmin / 2) as lat, lonmin + (lonmax - lonmin / 2) as lon, city, street, housenr, name FROM poicoord JOIN poidata ON poicoord.poiid = poidata.poiid JOIN poiname on poiname.docid = poicoord.poiid WHERE type = @category",
                connection))
            {
                command.Parameters.Add(new SQLiteParameter("category", DbType.Int32) { Value = category.Id });

                SQLiteDataReader reader = command.ExecuteReader();

                int latOrdinal = reader.GetOrdinal("lat");
                int lonOrdinal = reader.GetOrdinal("lon");
                int nameOrdinal = reader.GetOrdinal("name");
                int houseNrOrdinal = reader.GetOrdinal("housenr");
                int streetOrdinal = reader.GetOrdinal("street");
                int cityOrdinal = reader.GetOrdinal("city");

                while (reader.Read())
                {
                    pointsOfInterest.Add(new PointOfInterest()
                    { 
                        Latitude = reader.GetDouble(latOrdinal), 
                        Longitude = reader.GetDouble(lonOrdinal),
                        Name = reader.GetString(nameOrdinal),
                        HouseNumber = reader.IsDBNull(houseNrOrdinal) ? string.Empty : reader.GetString(houseNrOrdinal),
                        Street = reader.IsDBNull(streetOrdinal) ? string.Empty : reader.GetString(streetOrdinal),
                        City = reader.IsDBNull(cityOrdinal) ? string.Empty : reader.GetString(cityOrdinal),
                    });
                }
            }
        }

        return pointsOfInterest;
    }