diff --git a/index.py b/index.py
index 56772a9..0b0f9d5 100644
--- a/index.py
+++ b/index.py
@@ -189,7 +189,7 @@ def derive_marker_name(input: str) -> str:
 
     # merge metadata
 
-    occurrence_combined = pd.merge(occurrence_combined, metadata_df, on="materialSampleID", how="left")
+    occurrence_combined = pd.merge(occurrence_combined, metadata_df, on="materialSampleID", how="inner")
 
     # remove contaminants