Prabhupada's lecture - Śrīmad-Bhāgavatam 1.5.25 - Vṛndāvana, August 6, 1974
So here it is said that dvijaiḥ..., ucchiṣṭa-lepān anumodito dvijaiḥ. Dvijaiḥ, the brāhmaṇa... And the supreme brāhmaṇa is the devotee, kṛṣṇaika-śaraṇa. So Nārada Muni, in his previous birth, he was engaged in washing the dishes, eating the foodstuffs left by the dvijaiḥ, by the brāhmaṇas. In this way he infected their disease. As in ordinary material sense if you eat the remnants of foodstuff of a diseased fellow, then you infect that disease. Therefore sometimes when there is a patient suffering from tuberculosis, it is strictly separated from the family to another room or another house so that... It is very infectious.
Cholera is very infectious. Smallpox is very much infectious. There are many infectious disease. So as you infect this material disease by eating the foodstuff left by a diseased fellow, similarly, if you eat the remnants of foodstuff left by a Vaiṣṇava you become Vaiṣṇava. This is infection. So we should voluntarily accept this infection. The other infection we should avoid, but this infection we shall welcome. But the process is the same. Paraṁ dṛṣṭvā nivartate [Bg. 9.59]. You can refrain from the lower class of infection simply by infecting yourself with the higher class, or transcendental class of infection.