It is recommended that operators using particle counters track particles in the size range ______ because they are a possible surrogate for _______.

It is recommended that operators using particle counters track particles in the size range ______ because they are a possible surrogate for _______.

• A. 3-5 micrometers, Cryptosporidium
• B. 5-8 micrometers, Giardia
• C. 3-5 micrometers, Giardia
• D. 5-8 micrometers, Cryptosporidium

Answer: (A)

Using particle counts in a small size range as a proxy helps gauge the presence of certain pathogens without direct pathogen testing. Cryptosporidium oocysts are about 4–6 micrometers in diameter, so tracking particles in the 3–5 micrometer range provides a reasonable indicator of their occurrence in the water. Giardia cysts are larger, roughly 8–14 micrometers, so a 3–5 μm counter would miss much of Giardia and wouldn’t be a good surrogate for it. That’s why the 3–5 micrometer range is used as a surrogate for Cryptosporidium rather than Giardia.

Using particle counts in a small size range as a proxy helps gauge the presence of certain pathogens without direct pathogen testing. Cryptosporidium oocysts are about 4–6 micrometers in diameter, so tracking particles in the 3–5 micrometer range provides a reasonable indicator of their occurrence in the water. Giardia cysts are larger, roughly 8–14 micrometers, so a 3–5 μm counter would miss much of Giardia and wouldn’t be a good surrogate for it. That’s why the 3–5 micrometer range is used as a surrogate for Cryptosporidium rather than Giardia.