Trichomonads are a type of parasitic flagellate protozoan of the genus that are found in the digestive and reproductive systems of man and animals. They frequently colonize the human lungs, but this condition is unfamiliar to most physicians [
1,
2]. Several kinds of trichomonads can infect the lungs, such as
Trichomonas vaginalis, Trichomonas tenax, Pentatrichomonas hominis, and
Tetratrichomonas spp [
3‐
6]. At present, microscopic detection is the most common approach for testing trichomonads in the clinic. However, numerous factors can make their recognition very difficult, if not impossible. [
7,
8] First, immobility of trichomonads due to low temperature or for long periods in vitro can reduce the sensitivity. Second, many epithelial cells of lung alveoli move similarly to trichomonads, which could impede trichomonad detection [
1,
9]. Third, trichomonads can develop into an amoeboid form, making them unrecognizable [
10]. Therefore, there is an urgent need to establish a sensitive molecular method to diagnose pulmonary trichomoniasis. However, doing so is further complicated by the fact that numerous trichomonad species can infect human lungs. Existing gene based methods have been used to detect single types of trichomonads [
4,
11‐
13]. However, not all species can be tested at a single time. To overcome this issue, all 18S rRNA gene sequences of different kinds of trichomonads were downloaded from NCBI, and then the most conserved area of this gene was identified through sequence alignment. Primers were then designed to cover this conserved region. To determine the prevalence of
Trichomonas infection in the lungs, bronchoalveolar lavage fluids (BALF) from 115 cases were tested using nested PCR and microscopy. Furthermore, phylogenetic analysis was performed to determine which type of trichomonad is most likely to infect human lungs.