Perinatal mortality in kittens is not studied so information is limited. Kitten mortality is reported to be about 9.1% in the first 8 weeks, with no detailed figures for the first 48hrs postpartum. Most of the 9.1% are in the first week.
The disease is caused by bacteria in kittens can be grouped into those that are caught occur more commonly or those that are rare. We begin with those that are more common.
S. canis (group G) in cats is very common in the vagina of cats both from local vet clinics and in a research colony. First time queens remained colonized right up to parturition with higher numbers than older queens who seemed to clear a week or more before and first time queens recolonized sooner. So exposure was the issue. The kittens had antibodies from milk but they antibodies plummeted just before they died. The umbilical vein was infected extending to liver and sepsis. (Pat Blanchard pers comm)
Bacterial pneumonia occurs periodically in kittens and is one of the many causes of fading kitten syndrome. Gram-negative bacteria predominates and Highland et al (2009) reported on three kittens with E. coli pneumonia. These kittens had haemorrhagic or bloody fibrin OC's thoracic fluid and pulmonary consolidation. The pneumonia was necrotising and haemorrhagic with pleuritis.
Highland MA, Byrne BA, Debroy C, Samitz EM, Peterson TS, Oslund KL. (2009). Extraintestinal pathogenic Escherichia coli-induced pneumonia in three kittens and fecal prevalence in a clinically healthy cohort population. J Vet Diagn Invest 2009; 21(5): 609-615.
Sparkes AH, Rogers K, Henley WE, Gunn-Moore DA, May JM, Gruffydd-Jones TJ, Bessant C. (2006) A questionnaire-based study of gestation, parturition and neonatal mortality in pedigree breeding cats in the UK. J Feline Med Surg 2006; 8: 145-157