| Year | Month | Number of samples | |
|---|---|---|---|
| 2016 | April | 8 | 5 |
| May | 0 | 2 | |
| July | 1 | 0 | |
| November | 0 | 9 | |
| December | 10 | 9 | |
| 2017 | January | 0 | 3 |
| February | 0 | 2 | |
| March | 5 | 23 | |
| April | 7 | 10 | |
| May | 2 | 2 | |
| June | 4 | 6 | |
| July | 6 | 19 | |
| August* | 7 | 25 | |
| September | 7 | 10 | |
| October | 7 | 5 | |
| November | 6 | 5 | |
| December | 19 | 10 | |
| 2018 | March | 3 | 0 |
| November | 4 | 24 | |
| December | 0 | 1 | |