Streptococcus dysgalactiae

If you've recently had a baby and develop a fever or pelvic pain a few days later, this bacterium is one of the less familiar causes worth knowing about. It also turns up in women who aren't pregnant and have discharge, itching, or soreness that won't settle. Routine prenatal strep screening looks for a different species, so this one can go unnoticed.

This is an exploratory measurement. Your report shows how much of the organism was found on your vaginal swab, and no standardized cutpoints exist for how much is too much. The result is most useful when you read it alongside your symptoms, whether you're pregnant or recently delivered, and the rest of your vaginal microbiome.

What This Bacterium Is

S. dysgalactiae (Streptococcus dysgalactiae) belongs to the same genus as the germ behind strep throat. On a lab plate it breaks open red blood cells, and it carries surface markers that labs classify as group C or group G. In people, nearly all of what turns up belongs to one subspecies, equisimilis, which you'll often see abbreviated as SDSE.

Your body doesn't produce it. It's a bacterium that settles on moist linings, including the genital tract, and it can stay there for a while without causing symptoms. A healthy vagina is usually dominated by Lactobacillus, a group of bacteria that keeps the environment acidic and makes it harder for newcomers to take hold. Finding SDSE on your swab means an organism capable of causing infection is present, and the amount, your symptoms, and your life stage decide whether that matters.

Your result is reported in units of x10^5 CFU/ml, so the number is an estimate of bacterial load in hundreds of thousands per milliliter of sample. A colony-forming unit (CFU) is a culture term for one bacterial cell or clump that could grow into a colony. Labs that detect bacteria by their DNA often convert the signal into the same units, and this test's report doesn't state which approach was used.

Infection After Childbirth

The clearest evidence ties this organism to infections in the weeks after delivery. A Swedish population-based study followed 130 women with SDSE infections during pregnancy or within 42 days after birth, and these infections occurred in about 1 of every 1,000 births. The most common form was infection of the uterine lining (endometritis). Others included fever after delivery, wound infections, and infection of the membranes around the baby during labor.

Timing is the part to remember. In close to nine in ten of the endometritis cases, symptoms began more than 48 hours after delivery, which is often after a woman has gone home. None of the women became critically ill, and prompt antibiotics chosen for the organism led to recovery, though the infections still caused substantial illness.

That study had no comparison group, so it couldn't measure how often women who carry SDSE without symptoms go on to develop infection. The closest adjusted evidence comes from a better-studied relative, group B strep (GBS). Among 1,746 women swabbed at labor, those carrying GBS had roughly double the odds of infection around birth after adjustment (10.8% versus 6.3%). That finding is about GBS, and whether SDSE carries a similar risk hasn't been measured.

If you're late in pregnancy or recently delivered and you know SDSE is present, treat fever, worsening pelvic pain, or foul-smelling discharge two or more days after birth as a reason for same-day medical care. A positive swab tells you what to watch for, though it can't predict that infection will happen.

Vaginal Irritation and Discharge

Outside pregnancy, the evidence is thinner. In a study of women who had vaginal swabs taken in general practice, beta-hemolytic streptococci of groups A, C, and G were grouped together when looking for links with clinical vulvovaginitis. Vulvovaginitis is inflammation of the vulva and vagina, usually with discharge, itching, or soreness. The link was clearest for group A strep, and the study doesn't show that group C or G strep, which include SDSE, cause symptoms on their own. Heavy, pure growth was the pattern the authors flagged, and they recommended that labs identify the organism and test which antibiotics work against it when it appears that way in a woman with symptoms.

This is where knowing the amount helps. A small amount on a swab from someone without symptoms reads very differently from a large amount in someone with discharge that yeast or bacterial vaginosis treatment hasn't cleared. That study graded growth on culture plates, so how its heavy growth maps onto the number on your report hasn't been studied.

When the Infection Spreads

Once SDSE gets past a mucosal barrier it can cause infections that look like those from the strep throat bacterium: bloodstream infection, deep soft-tissue infection, flesh-destroying infection, and a toxic shock-like illness. In a Japanese nationwide study of 278 people with invasive SDSE, about one in eight died within 28 days, rising to about one in six among those 80 and older.

In Finland, people with diabetes had about five times the odds of SDSE bloodstream infection compared with people without it, and obesity and coronary artery disease also raised the odds. These studies looked mostly at older adults with invasive disease and don't show that vaginal carriage leads to bloodstream infection. They do show what the organism can do, which is the reason to take symptoms seriously when your swab is positive and you have diabetes, a recent delivery, or a wound in the genital area.

Resistance to Common Antibiotics

Some SDSE recovered from women's vaginal swabs in a Gambian trial carried genes for resistance to macrolides, the antibiotic family that includes azithromycin and erythromycin. Some of those strains also displayed the group A marker, so standard typing made them look like the strep throat bacterium.

Among genital streptococci more broadly (mostly GBS), penicillin generally still works, while resistance to clindamycin and erythromycin is common and varies widely between regions and studies. If you need treatment and have a penicillin allergy, a culture with susceptibility testing on the isolate is the way to choose between the alternatives.

Why It Gets Mixed Up With Other Strep

Prenatal strep screening is built for GBS. Molecular GBS tests amplify genes found only in that species, and the colored culture plates used for GBS screening are tuned to its reactions, so both can miss SDSE entirely. Common multi-target vaginitis panels look for yeast, Trichomonas, and the bacteria behind bacterial vaginosis, and they usually leave out this kind of strep as well.

Labs can also confuse SDSE with group A strep, because some strains carry the group A marker. A negative GBS screen or a normal vaginitis panel therefore tells you nothing about whether SDSE is present.

When Results Can Be Misleading

Studies of genital strep, mostly GBS, show that carriage in the reproductive tract can come and go over weeks, so one swab may catch it on a good or bad day.

• Shifting carriage: strep can appear and disappear between swabs taken a few weeks apart, so a single positive or negative result may not hold.
• Cycle timing: the mix of vaginal bacteria changes across the menstrual cycle, so swabs taken at different points in your cycle aren't directly comparable.
• Low amounts and contaminants: in studies of molecular GBS tests, small bacterial loads produced false negatives, and blood, mucus, or lubricant on the swab interfered with the test. Similar problems are likely for SDSE but haven't been studied directly.
• Method differences: labs measure vaginal bacteria in different ways, and in GBS studies culture without an enrichment step missed a substantial share of true cases. Numbers from different labs or methods can't be compared directly.

Tracking Your Trend

Because carriage fluctuates, repeated swabs tell you far more than one. Two positives weeks apart suggest an established presence, while a single positive followed by negatives fits passing carriage. A series also shows whether the amount rises when symptoms appear and falls when they resolve, which is the closest thing to a personal threshold this marker offers. The evidence that probiotics or diet lower this specific species is indirect, so retesting is how you find out whether anything changed in your case.

What to Do With a Positive Result

How you act depends on the combination of findings more than on the number alone.

• Positive with symptoms: get a culture with antibiotic susceptibility testing and see a gynecologist or primary care clinician, since treatment requires a prescription chosen for the isolate.
• Positive while pregnant or after delivery: tell your obstetric team now, and seek same-day care for fever or pelvic pain after birth.
• Positive without symptoms, not pregnant: retest within 3 months at the same cycle phase, since no study shows that treating carriage without symptoms improves outcomes.
• Positive with low Lactobacillus or a high vaginal pH: this pattern points toward a disturbed vaginal microbiome overall, so review the aerobic vaginitis and bacterial vaginosis results on the same panel and add sexually transmitted infection testing if you have discharge.