TORCH Infections
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Direct answer
TORCH infections are a group of pathogens that cross the placenta and cause congenital disease, named for Toxoplasma, Rubella, Cytomegalovirus and Herpes simplex, with "Others" covering syphilis, varicella, parvovirus B19, HIV, hepatitis B and listeria. Cytomegalovirus is the commonest congenital viral infection, causing hearing loss and periventricular calcification. The panel is used to assess a newborn with suspected congenital infection, and the right test depends on the timing of infection.
What you must remember
- Toxoplasma: Acquired from undercooked meat or cat faeces, and congenital toxoplasmosis classically causes chorioretinitis, hydrocephalus and intracranial calcification.
- Rubella: Infection in early pregnancy causes cataract, congenital heart disease and sensorineural deafness, and rubella IgM in the infant's serum confirms the diagnosis.
- Cytomegalovirus: The commonest congenital viral infection, causing sensorineural hearing loss, microcephaly, periventricular calcification and hepatosplenomegaly.
- Herpes simplex: Neonatal infection is usually acquired in an infected birth canal and presents as skin, eye or mouth vesicles, encephalitis or disseminated disease.
- Syphilis: Congenital syphilis features Hutchinson teeth, mulberry molars, saddle nose and interstitial keratitis, and it is diagnosed by treponemal and non-treponemal serology.
- Varicella and parvovirus B19: Early maternal varicella can cause congenital varicella syndrome, while parvovirus B19 can cause hydrops fetalis and fetal anaemia.
- Listeria: This Gram-positive bacillus can cause granulomatosis infantiseptica and neonatal sepsis after transplacental or birth-canal spread.
- Timing rule: Congenital infection is confirmed by IgM in the infant's own serum or by PCR, because maternal IgG crosses the placenta and proves nothing about the infant.
Pathogen-by-pathogen features
The TORCH label is a teaching aid, and the diagnostic clue for each pathogen is what exams test. The table sets out the key feature and clue for the six infections most often asked.
| Pathogen | Key congenital feature | Diagnostic clue |
|---|---|---|
| Toxoplasma | Chorioretinitis, hydrocephalus, calcification | IgM, IgG avidity, amniotic fluid PCR |
| Rubella | Cataract, heart disease, deafness | Rubella IgM in infant serum |
| Cytomegalovirus | Hearing loss, periventricular calcification | Urine or saliva PCR within 21 days |
| Herpes simplex | Skin, eye and mouth vesicles, encephalitis | HSV PCR from lesions or CSF |
| Syphilis | Hutchinson teeth, mulberry molars, saddle nose | Treponemal and non-treponemal tests |
| Parvovirus B19 | Hydrops fetalis, fetal anaemia | Maternal IgM and fetal ultrasound |
Rubella and cytomegalovirus are the two most tested for classic defect patterns, and the timing of maternal infection matters more than the test name. Congenital toxoplasmosis is treated with spiramycin and then pyrimethamine with sulfadiazine in many guidelines, which is worth remembering for therapy questions.
IgM in the newborn, IgG avidity and PCR together separate congenital from maternal and postnatal infection. An IgG-positive baby does not prove infection, because maternal IgG crosses the placenta freely.
Where the exam tries to catch you
TORCH questions usually hinge on the interpretation of antibodies and on the timing of the test.
- Trap: Reading IgG in a newborn as proof of infection Correct: Maternal IgG crosses the placenta, so only IgM in the infant's serum or a positive PCR indicates congenital infection.
- Trap: Testing a newborn for CMV with a late sample Correct: Urine or saliva PCR must be taken within about 21 days of birth, since later samples cannot separate congenital from postnatal infection.
- Trap: Assuming congenital CMV always looks obvious at birth Correct: Most infected newborns appear well, and hearing loss can emerge later, so screening matters.
Frequently asked questions
What does the TORCH acronym stand for?
TORCH stands for Toxoplasma, Rubella, Cytomegalovirus and Herpes simplex virus, and "Others" covers syphilis, varicella, parvovirus B19, HIV, hepatitis B and listeria. It is a teaching and screening label for infections that cross the placenta.
Which congenital infection causes hydrocephalus with intracranial calcification?
Congenital toxoplasmosis classically causes chorioretinitis, hydrocephalus and intracranial calcification. This triad is a common exam pattern, and the diagnosis is supported by IgM, IgG avidity and PCR.
Which TORCH infection is the commonest congenital viral infection?
Cytomegalovirus is the commonest congenital viral infection and can cause sensorineural hearing loss, microcephaly and periventricular calcification. Urine or saliva PCR within 21 days of birth distinguishes congenital from postnatal infection.
How is neonatal herpes simplex usually acquired?
Neonatal herpes simplex is usually acquired during passage through an infected birth canal, when the mother has active genital lesions. It presents with skin, eye or mouth vesicles, encephalitis or disseminated disease, and it is treated with intravenous aciclovir.
Which features suggest congenital syphilis in a newborn?
Congenital syphilis features Hutchinson teeth, mulberry molars, saddle nose and interstitial keratitis, and it is diagnosed by treponemal and non-treponemal serology. Screening and treatment of the mother during pregnancy prevent most cases.