Haemophilus influenzae

Background

Haemophilus influenzae (H. influenzae) are bacteria commonly carried in the respiratory tract, which can cause acute invasive disease. They are divided into encapsulated and unencapsulated (non-typeable) strains. Encapsulated strains can be classified into six serotypes, from a to f, of which type b (Hib) was most prevalent prior to vaccine introduction. Infection with H. influenzae can cause the following conditions:

  • meningitis
  • septicaemia
  • acute respiratory infections

Less frequent conditions which may be caused by H. influenzae infection include:

  • epiglottitis
  • osteomyelitis
  • septic arthritis

For more information on H. influenzae, visit the NHS inform website.

Guidance

Guidance on Haemophilus influenzae can be found below:

For all infection prevention and control guidance visit the A-Z ​pathogens section of the National Infection and Prevention Control Manual.

Data and surveillance

In 1992, following introduction of the Hib vaccine for young children, the number of H. influenzae type b cases fell dramatically, not only in the vaccinated group but also in older age groups.  Due to reduced carriage of the organism within the respiratory tract of vaccinated children, transmission to the wider community was effectively suppressed. The addition of the Hib booster vaccine in 2006, reduced case numbers further.

In Scotland, typing is conducted on  all cases with positive laboratory reports for H. influenzae, in order that national trends in disease subtypes can be monitored. Further enhanced surveillance is carried out for all H. influenzae cases identified in children under the age of 5 and type b strains across all age groups.

Surveillance update for 2018

Between October and December 2018 (weeks 40 to 52), 23 cases of invasive H. influenzae were reported, bringing the total number of cases for 2018 to 82. This is comparable to annual cumulative case numbers reported over the previous ten years which ranged from 46 to 99 cases, as shown in Figure 1.

Of the 82 cases reported in 2018:

  • Nine, which is 11%, were aged under five years
  • three, which is 3.7%, were aged between 11 to 20 years
  • ten, which is 12.2%, were aged between 21 to 40 years
  • 60, which is 73.1%, were above 40 years of age

Information on clinical presentation was available for eight of the ten reported paediatric (under 16 years old) cases and included:

  • bacteraemia
  • fever
  • respiratory symptoms
  • gastro-intestinal symptoms

Figure 1 is a line graph showing cumulative (week 1 to 52) number of H. influenzae cases reported to HPS per week by year. Each line represents a different year from 2008 to the fourth quarter of 2018 and all years show a steady increase in cumulative number of cases per week. Fewer cases were observed in 2018 when compared with 2017 (which had the highest number of annual cases since 2008, however the only other year which had higher case numbers than 2018 was 2015.

Of the 82 invasive cases reported in 2018:

  • 74, which is 90.2%, had H. influenzae isolated from blood
  • three, which is 3.7%, from cerebrospinal fluid
  • five, which is 6.1%, from pleural fluid

Three cases are known to have died in 2018, which is slightly increased in comparison to annual figures over the previous five years (0 to 1 deaths per year).

Figure 2 demonstrates the epidemiological impact of the Hib vaccine, for those aged under five (routinely vaccinated group) and for all ages (including under fives). Prevalence has shown a corresponding decrease in cases since 1992 and figures have remained relatively stable since 2011.

Figure 2 is a line graph showing the number of invasive H. influenzae type b disease cases reported to HPS from 1988 to the fourth quarter of 2018. There are two lines on the graph, one representing the under 5 age group and the other, total number of cases (including under 5 years). Following introduction of the Hib vaccine in 1992, cases rapidly decreased to single figures. However in 2001 a sharp increase was observed and total number of cases peaked at 31 in 2002, prompting introduction of the Hib booster campaign in June 2003. Cases across all ages subsequently decreased and following introduction of a routine Hib booster in 2006, reached low numbers by 2009. Only one case has been observed in the under 5 age group between 2011 and fourth quarter of 2018.

Figure 3 presents laboratory reports by serotype, since the introduction of the Hib booster campaign in 2003.

In 2018, H. influenzae type was available for 61 (74.4%) isolates, of which:

  • 47, which is 77%, were non-typeable (NT)
  • six, which is 9.8%, were type f
  • two, which is 3.3%, were type a
  • one, which is 1.6%, was type b
  • five, which is 8.2%, were type e

H. influenzae type was available for seven of the ten paediatric cases:

  • four were non-typeable
  • two were type e
  • one was type f

During this period, there has been a marked increase in the number of non-typeable (NT) isolates, although proportionally the percentage has remained stable from 2017 to 2018. Proportionally, there was a reduction in the number of cases for which typing was not available, from 36.4% in 2017 to 25.6% in 2018. Prior to 2016 (when one case was reported), laboratory confirmation of type a had not been recorded for any H. influenzae cases in Scotland, however in 2018 two type a cases were reported in older adults (over 60 years of age).

Figure 3 is a bar chart showing the laboratory reports of H. influenzae by type from 2003 to the fourth quarter of 2018. The chart shows a steady decline in type b infection since introduction of the Hib vaccine in 2003, with a corresponding increase in non-typeable (NT) strains. Non-typeable strains are now the most commonly reported type, with very few reports of types a, d, e and f. Type a had not been recorded in Scotland prior to 2016 (when one case was reported) and two cases were observed in 2018.

Surveillance form

View the surveillance of invasive Haemophilus influenzae infection form

Vaccine Uptake Statistics

Vaccine uptake statistics can be found on the Information Services Division (ISD) website.