A 27-year-old woman from Mali presents with pruritus and a papular rash on her shoulders. She lives near a fast-flowing river. Skin snips from the iliac crest and shoulder are taken and incubated in saline for 24 hours. Microfilariae are counted. This test is used to determine microfilarial load. What is the minimum community microfilarial prevalence threshold at which WHO recommends mass drug administration (MDA) with ivermectin for onchocerciasis?