Epidemiology of Genital Mycoplasmas

A group of pathogenic microorganisms generally known as genital mycoplasmas, that were identified as early as 1898, are frequently encountered in the lower genitourinary tract of sexually active men and women. Although their prevalence might be high among healthy people, they are also responsible for various infectious syndromes and potential complications.

Mycoplasmas are considered the smallest free-living organisms. They are neither bacteria nor viruses, and they do not possess a cell wall (which is why they can occur in a plethora of different shapes). All genital mycoplasmas found in humans belong to the family Mycoplasmataceae within the class Mollicutes.

Common Inhabitants of the Genital Tract

After puberty, the colonization of both male and female lower genital tract by Ureaplasmaspp. and Mycoplasma hominis occurs as a consequence of sexual activity. Hence between 40-80% and 21-53% of asymptomatic and sexually active women harbor Ureaplasma spp. and Mycoplasma hominis, respectively. This prevalence is somewhat lower in men.

These percentages are highly related to the number of sex partners. Studies have shown that Mycoplasma hominis can be isolated in approximately 16% of women with multiple life partners, compared to 2% in women with no sexual history. Such patients are classified as carriers.

On the other hand, Mycoplasma genitalium is usually detected in men with non-gonococcal urethritis that is not chlamydial in origin. In this group of patients the prevalence of Mycoplasma genitalium ranges from 13% to 42%, and in asymptomatic men from 0% to 15%. In symptomatic women Mycoplasma genitalium can be found in up to 42% cases.

Ureaplasma species can colonize more than 20% of infants, and those born before term are especially prone to colonization. This incidence generally declines after the third month of life. Only about 5% of children and 10% of prepubertal females are colonized with genital mycoplasmas.

In the majority of healthy adults genital mycoplasmas primarily exist as commensals associated with the mucosa, and thus they rarely result in serious invasive disease. Nevertheless, in immunocompromised individuals, and especially if hypogammaglobulinemia is present, the invasion of extragenital sites may be seen.

Routes of Transmission

All genital mycoplasmas are transmitted horizontally via sexual contact, albeit their roles in genital tract disease vary significantly. Today we know that these organisms can cause non-gonococcal urethritis in men and women alike, as well as cervicitis, bacterial vaginosis and endometritis in women.

Still, the vertical route remains a very important route of transmission that warrants medical attention. This means transmission from a colonized woman to her infant – either in utero (transplacentally or by ascending infection from the birth canal) or during delivery (by passing through a colonized birth canal).

The rate of vertical transmission may be up to 55% in both full-term and preterm infants, and it is not affected by the chosen method of delivery (though it may be substantially increased when chorioamnionitis is present). Moreover, rates of colonization are usually higher in newborns with very low birth weight.

Genital mycoplasmas are habitually isolated from gravid women with similar recovery rates as in non-pregnant women that exhibit the same degree of sexual activity. Since pregnant women (and preterm infants) are groups with an altered immune status, it does not come as a surprise that these microorganisms can sometimes result in invasive and destructive forms of disease.

References

• http://jcm.asm.org/content/42/10/4636.full
• https://www.ncbi.nlm.nih.gov/pubmed/17401188
• https://www.ncbi.nlm.nih.gov/pubmed/19821660
• http://eknygos.lsmuni.lt/springer/599/271-288.pdf
• https://www.hindawi.com/journals/jpath/2014/183167/
• http://journals.sagepub.com/doi/abs/10.1258/0956462021924695?journalCode=stda
• Mendoza N, Ravanfar P, Shetty AK, Pellicane BL, Creed R, Goel S, Tyring SK. Genital Mycoplasma Infection. In: Gross G, Tyring SK, editors. Sexually Transmitted Infections and Sexually Transmitted Diseases. Springer Science & Business Media, 2011; pp. 197-202.
• Martin DH. Genital Mycoplasmas: Mycoplasma genitalium, Mycoplasma hominis and Ureaplasma Species. In: Bennett JE, Dolin R, Blaser MJ, editors. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. Elsevier Health Sciences, 2015; pp. 2190-2193.