Microbiology
Pathogens
A 21 year old male patient attends ED with a profuse thick green urethral discharge and dysuria. What is the most likely causative pathogen:
Answer:
The most likely diagnosis is gonorrhoea, caused by Neisseria gonorrhoeae, given the symptoms of a profuse purulent discharge. Causes of non-gonococcal urethritis (NGU) in men include Chlamydia trachomatis (accounts for about 50% of cases), Trichomonas vaginalis, Herpes simplex, Mycoplasma genitalium, Adenovirus, Ureaplasma urealyticum and Haemophilus vaginalis.Neisseria Gonorrhoeae
Microbiology / Pathogens / Neisseria
Last Updated: 1st December 2023
| Microorganism | Neisseria Gonorrhoeae |
|---|---|
| Gram stain | Gram negative |
| Shape | Cocci (diplococci) |
| Oxygen requirements | Obligate aerobe |
| Additional features | Only ferments glucose |
| Transmission | Sexual and peripartum |
| Diseases | Urethritis, epididymo-orchitis, PID, septic arthritis, endocarditis, neonatal conjunctivitis |
Transmission
Neisseria gonorrhoeae causes gonorrhoea, a sexually transmitted infection most common in individuals between 15 and 35 years of age, and may also cause ophthalmia neonatorum through peripartum transmission.
Clinical Disease
The organism adheres to the genitourinary epithelium via pili, then invades the epithelial layer, triggering a local acute inflammatory response. It may affect the mucous membranes of the urethra, endocervix, rectum, oropharynx, and conjunctiva.
Clinical features may include:
- Local infection
- Acute painful urethritis, dysuria and purulent urethral discharge in men (urethral infection is symptomatic in about 90% of men)
- Vaginal discharge, irregular bleeding, dyspareunia and dysuria in women (but endocervical/urethral infection is asymptomatic in about 50% of cases)
- Pharyngitis in pharyngeal infection
- Anal pruritus, pain, tenesmus, discharge or bleeding in rectal infection
- Purulent conjunctivitis in ocular infection
- Disseminated infection
- Gonococcal bacteraemia
- Septic arthritis
- Dermatitis (pustular rashes)
- Gonococcal endocarditis
- Reactive arthritis
Complications include:
- Men
- Epididymo-orchitis, penile lymphangitis, periurethral abscess, acute prostatitis, seminal vesiculitis, urethral scarring and stricture causing bladder outflow obstruction
- Women
- Bartholin's abscess, pelvic inflammatory disease, infertility, chronic pelvic pain, ectopic pregnancy, perihepatitis, pregnancy-related complications
Diagnosis
Diagnosis is with NAAT, microscopy or culture of a first pass urine sample or urethral swab in men and urethral or endocervical swabs in women +/- rectal/pharyngeal swabs if indicated.
Treatment
If diagnosis is suspected from clinical features, the patient should be treated empirically whilst waiting for laboratory confirmation. Ideally, a culture should be taken before prescribing antibiotics, to test for susceptibility and identify resistant strains.
For people with uncomplicated anogenital or pharyngeal infection:
- When the antimicrobial susceptibility is known prior to treatment, prescribe ciprofloxacin 500 mg orally as a single dose.
- When antimicrobial susceptibility is not known prior to treatment, prescribe ceftriaxone 1 g intramuscular (IM) injection as a single dose.
Alternative treatments are recommended for people with an allergy, needle phobia, or other contraindications. These include gentamicin 240 mg IM as a single dose plus azithromycin 2 g orally OR cefixime 400 mg orally as a single dose plus azithromycin 2 g orally (advisable only if an IM injection is contraindicated or refused by the person). When using alternative regimens without antibiotic susceptibility data, it is recommended to regularly review local and national trends in gonococcal antimicrobial resistance.
A test of cure and contact tracing is recommended for all people who have been treated for gonorrhoea.
Prevention
Prevention of gonorrhoea involves the use of condoms, avoidance of high risk sexual behaviour and the prompt treatment of symptomatic patients and their contacts.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
