Objective:To investigate the etiology, clinical characteristics and outcome of severe pneumonia-associated hemophagocytic lymphohistiocytosis, and to analyze the risk factors for mortality.Methods:Clinical data of patients with severe pneumonia-associated hemophagocytic lymphohistiocytosis admitted to Shenzhen Children′s Hospital from February 2009 to February 2019 were retrospectively analyzed.The data included clinical characteristics, etiology, clinical manifestations, laboratory data, treatment and outcomes of the patients.The clinical characteristics and laboratory data of the survival group and the death group were compared by independent sample t-test. Results:(1) Clinical characteristics: the patients were aged from 3 months to 8 years and 7 months, including 15 males and 15 females.Severe pneumonia-associated hemophagocytic lymphohistiocytosis accounted for 2.74% (30/1 096 cases) of severe pneumonia in the same period.(2) Etiology: Mycoplasma pneumoniae infection was found in 8 cases (8/30 cases, 26.67%), virus infection in 7 cases (7/30 cases, 23.33%, including 5 cases with adenovirus infection, 1 case with EB virus infection, and 1 case with cytomegalovirus infection), Mycoplasma pneumoniae complicated with adenovirus infection in 4 cases (4/30 cases, 13.33%), bacterial infection in 3 cases (3/30 cases, 10%), and fungal infection in 2 cases, Mycobacterium tuberculosis infection in 1 case.The pathogens were not identified in 5 patients.(3) Clinical manifestations: fever and hepatomegaly were present in all patients.Besides, 86.67% (26/30)patients had fever duration more than 10 days, 83.33% (25/30 cases) patients had cough, 76.66% (23/30 cases) patients had splenomegaly, and 33.33% (10/30 cases) patients had nervous system symptoms.Laboratory data showed varying degrees of reduction of binary and ternary systems in 80.00%(24/30 cases) of the patients.Liver function impairment was found in half of the patients, and serum ferritin and lactate dehydrogenase levels were elevated in all patients.(4) The mortality rate was 30.00% (9/30 cases). The differences in age, hypertriglyceridemia and high serum ferritin levels between the survival and death groups were significant (all P<0.05). Conclusions:Severe pneumonia-associated hemophagocytic lymphohistiocytosis is a disease with a high mortality rate.Patients with Mycoplasma pneumoniae and adenovirus pneumonia are more likely to suffer from secondary hemophagocytic lymphohistiocytosis.Younger age, hypertriglyceridemia and high serum ferritin levels are indicative of poor prognosis.

Multisystem inflammatory syndrome in children (MIS-C) reported in the United States and European countries is a disease with multi-organ involved symptoms related with 2019 Novel Coronavirus infection, which has never been reported in China.Although its symptoms are similar to Kawasaki disease, MIS-C has characteristics of higher frequency in older children and adolescents, gastrointestinal symptoms, haemodynamic instability, myocarditis and elevated inflammatory markers.Most of the children need intensive care.The pathogenesis and long-term prognosis of the disease need further study.