Microbiology
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Pathogens
A full term 6 day old neonate is brought in with a unilateral eye purulent discharge which the parents noticed earlier that day. On gram stain of the exudate, no bacteria are seen. Which of the following is the most likely causative pathogen:
Answer:
Ophthalmia neonatorum refers to any conjunctivitis occurring in the first 28 days of life, and in the UK is most commonly caused by Chlamydia trachomatis, which does not typically show up on Gram stain (unlike Neisseria gonorrhoeae which stains Gram negative).Chlamydia Trachomatis and other Chlamydial species
Microbiology / Pathogens / Chlamydia
Last Updated: 9th January 2024
| Microorganism | Chlamydia trachomatis |
|---|---|
| Features | Obligate intracellular bacterium |
| Reservoir | Individuals with asymptomatic genital tract infection |
| Transmission | Sexual and peripartum |
| Diseases | Chlamydia, trachoma, conjunctivitis, ophthalmia neonatorum, pneumonia |
Members of the Chlamydia spp. are small, nonmotile, Gram-negative, obligate intracellular organisms that grow in the cytoplasm of host cells.
Chlamydia trachomatis is implicated predominantly in infections of the genital tract (chlamydia, lymphogranuloma venereum) but also of the eye (conjunctivitis, trachoma, ophthalmia neonatorum) and occasionally of the lungs (typically neonatal pneumonia). Chlamydia trachomatis infects only humans and is primarily transmitted sexually or peripartum.
Clinical Disease
Chlamydia is the most common sexually transmitted infection in the UK and the most common preventable cause of infertility worldwide. It is most commonly asymptomatic (in approx. 50% of men and 80% of women), but may present with pelvic pain, vaginal discharge, dysuria, intermenstrual/postcoital bleeding or dyspareunia in women, or with urethritis with dysuria and urethral discharge in men.
Diagnosis
Diagnosis is usually by nucleic acid amplification tests (NAATs) although enzyme immunoassays (EIAs) and cell culture techniques are available. Samples should be taken as vulvovaginal/endocervical swabs or first-void urine samples in women or first-void urine samples in men. Pharyngeal or rectal swabs may be required as indicated.
Treatment
First line treatment for uncomplicated genital chlamydia infection is with azithromycin (single 1 g dose) or doxycycline (100 mg bd for 7 days). Erythromycin is an alternative.
Contact tracing is recommended.
Complications
Complications of chlamydia include:
- Women
- Pelvic inflammatory disease
- Perihepatitis as part of Fitz-Hugh and Curtis syndrome
- Ectopic pregnancy
- Tubal infertility
- Chronic pelvic pain
- If pregnant - premature rupture of membranes, preterm delivery and low birth weight
- Neonatal ophthalmic infection/pneumonia secondary to peripartum transmission
- Men
- Urethral stricture and scarring
- Epididymo-orchitis
- Prostatitis
- Immune-mediated
- Reactive arthritis (Reiter’s syndrome is a triad of urethritis, arthritis and conjunctivitis which can be triggered by chlamydial infection)
Prevention
Prevention of infection can be achieved by the use of condoms, prompt treatment of both the patient and their sexual contacts, and screening for and treatment of concomitant STIs.
Ophthalmia Neonatorum
Ophthalmia neonatorum refers to any conjunctivitis occurring in the first 28 days of life. Conjunctivitis appears in about 20 - 50% of infants exposed to C. trachomatis infecting the cervix at birth; chlamydia is the single most common cause of ophthalmia neonatorum in the UK (although gonorrhoeal conjunctivitis has more severe sequelae). Affected babies present with mucopurulent discharge from one or both eyes usually within 5 – 14 days. There may be associated preseptal cellulitis and, less commonly, rhinitis, otitis and pneumonitis. Complications can include keratitis, conjunctival scarring and permanent visual impairment.
Chlamydial Pneumonias
Chlamydia trachomatis can also cause pneumonia, primarily in infants and young children.
Two other chlamydial organisms may also cause pneumonia in humans:
Chlamydophila pneumophila infects only humans, is transmitted by aerosol and may cause upper and lower respiratory tract infections, especially bronchitis and pneumonia in young adults.
Chlamydophila psittaci infects birds and many mammals. Humans are infected primarily by inhaling organisms in dry bird faeces. Psittacosis may be asymptomatic or may produce high fever and pneumonia associated with headache, altered mental state, and hepatosplenomegaly.
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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 |
