Sepsis neonatorum, or neonatal sepsis, is an invasive infection that occurs in newborns. Two classes of the disease are distinguished: early-onset sepsis, which usually strikes within the first 24 hours after birth, and late-onset sepsis, which occurs after the fourth day of life. While the organisms causing the infection in the early-onset disease are obtained from the mother, often at the time of passing through the birth canal, the microbes responsible for late-onset sepsis are picked up from the external environment, which is often the hospital.
Neonatal sepsis is a frequent cause of neonatal mortality; unfortunately, the symptoms of sepsis are not specific and may be attributed to other, noninfectious, causes. It is, therefore, crucial to pay attention to the risk factors for neonatal sepsis.
For early-onset infections, the maternal status of colonization by microorganisms and associated factors are the most important predictors of sepsis in neonates. Infection by group B streptococcus (GBS) species is the most frequent cause of neonatal sepsis, although the prophylactic antibiotic administration has decreased its incidence. Escherichia coli is another common cause of early-onset infections, followed in frequency by other organisms, such as haemophilus influenzae. Organisms such as GBS can invade the amniotic fluid during labor or through occult tears, and cause chorioamnionitis. Women with premature rupture of membranes are also at high risk for colonization of the amniotic fluid, as are those who have preterm labor. All of the above factors can suggest risk for sepsis in the newborn  . In one study, women in preterm labor and with premature rupture of membranes were found to have a 75% incidence of microbial invasion of the amniotic cavity .
The most important risk factor for late-onset sepsis is the gestational age at delivery: premature newborns are at increased risk because of a weak immune system, or procedures utilizing invasive devices. The most common agent of late-onset sepsis is the group of coagulase-negative staphylococci, major nosocomial pathogens.
Initial signs of neonatal sepsis include decreased activity, feeding and breathing difficulties, abnormal temperature (too high or too low), and diarrhea or vomiting. Hypoglycemia, hyperglycemia, and metabolic acidosis often accompany sepsis, but also occur in purely metabolic conditions. Pneumonia, whether of intrauterine or intrapartum origin, may not be easy to differentiate from respiratory distress syndrome. Coughing, irregular respiration, decreased breath sounds and other symptoms characterize both diseases. Neurological signs (changes in consciousness, seizures, and others) are characteristic of meningitis, which is the common form of central nervous system infection in neonatal sepsis.
Early diagnosis is critical for starting therapy. The pathogen should be identified as soon as possible, so that the treatment with broad-spectrum antibiotics, which carries potential risks if continued too long, can be replaced by a regimen using more specific agents. Analysis of the complete blood cell count with differentials, together with cultures of blood, cerebrospinal fluid and urine (the latter only for late-onset sepsis) are performed in suspected cases.
Thrombocytopenia  and neutropenia  are frequently observed but are not specific signs. The immature to total neutrophil ratio is a more sensitive indicator of sepsis . Sepsis screening panels use a variety of indicators, including leukocyte counts, neutrophil counts and immature to total neutrophil ratios ; their positive predictive value is highly diagnostic.
Blood cultures should test for both aerobic and anaerobic bacteria; growth usually occurs within two days. Results from tests using the polymerase chain reaction (PCR) are available in five hours . Testing for herpes simplex virus is also done by PCR in cases where there is a strong indication of infection by the virus.
Of the acute phase proteins, C-reactive protein and procalcitonin have been used most extensively  . A raised procalcitonin level 24 hours after birth is a good indicator of sepsis .
Analysis of the cerebrospinal fluid shows increased protein concentration and white blood cell count and decreased glucose concentration in case of meningitis. Cerebrospinal fluid culture should be obtained in cases of suspected sepsis if lumbar puncture can be performed. If the culture shows bacterial growth, further samples should be taken to follow the course of the disease and the effectiveness of treatment.
Chest radiography and imaging of the head by computed tomographic scan, magnetic resonance imaging, or ultrasonography are performed as needed.